Prepare for separation of RSpec helper files

Since rspec-rails 3, the default installation creates two helper files:
* `spec_helper.rb`
* `rails_helper.rb`

`spec_helper.rb` is intended as a way of running specs that do not
require Rails, whereas `rails_helper.rb` loads Rails (as Discourse's
current `spec_helper.rb` does).

For more information:

https://www.relishapp.com/rspec/rspec-rails/docs/upgrade#default-helper-files

In this commit, I've simply replaced all instances of `spec_helper` with
`rails_helper`, and renamed the original `spec_helper.rb`.

This brings the Discourse project closer to the standard usage of RSpec
in a Rails app.

At present, every spec relies on loading Rails, but there are likely
many that don't need to. In a future pull request, I hope to introduce a
separate, minimal `spec_helper.rb` which can be used in tests which
don't rely on Rails.

spec/rails_helper.rb

@@ -0,0 +1,182 @@
+if ENV['COVERAGE']
+  require 'simplecov'
+  SimpleCov.start
+end
+
+require 'rubygems'
+require 'spork'
+require 'rbtrace'
+#uncomment the following line to use spork with the debugger
+#require 'spork/ext/ruby-debug'
+
+require 'fakeweb'
+FakeWeb.allow_net_connect = false
+
+Spork.prefork do
+  # Loading more in this block will cause your tests to run faster. However,
+  # if you change any configuration or code from libraries loaded here, you'll
+  # need to restart spork for it take effect.
+  require 'fabrication'
+  require 'mocha/api'
+  require 'fakeweb'
+  require 'certified'
+
+  ENV["RAILS_ENV"] ||= 'test'
+  require File.expand_path("../../config/environment", __FILE__)
+  require 'rspec/rails'
+  require 'shoulda'
+
+  # Requires supporting ruby files with custom matchers and macros, etc,
+  # in spec/support/ and its subdirectories.
+  Dir[Rails.root.join("spec/support/**/*.rb")].each {|f| require f}
+  Dir[Rails.root.join("spec/fabricators/*.rb")].each {|f| require f}
+
+  # let's not run seed_fu every test
+  SeedFu.quiet = true if SeedFu.respond_to? :quiet
+
+  SiteSetting.automatically_download_gravatars = false
+
+  SeedFu.seed
+
+  RSpec.configure do |config|
+    config.fail_fast = ENV['RSPEC_FAIL_FAST'] == "1"
+    config.include Helpers
+    config.include MessageBus
+    config.include RSpecHtmlMatchers
+    config.mock_framework = :mocha
+    config.order = 'random'
+    config.infer_spec_type_from_file_location!
+
+    # If you're not using ActiveRecord, or you'd prefer not to run each of your
+    # examples within a transaction, remove the following line or assign false
+    # instead of true.
+    config.use_transactional_fixtures = true
+
+    # If true, the base class of anonymous controllers will be inferred
+    # automatically. This will be the default behavior in future versions of
+    # rspec-rails.
+    config.infer_base_class_for_anonymous_controllers = true
+
+    config.before(:suite) do
+
+      Sidekiq.error_handlers.clear
+
+      # Ugly, but needed until we have a user creator
+      User.skip_callback(:create, :after, :ensure_in_trust_level_group)
+
+      DiscoursePluginRegistry.clear if ENV['LOAD_PLUGINS'] != "1"
+      Discourse.current_user_provider = TestCurrentUserProvider
+
+      SiteSetting.refresh!
+
+      # Rebase defaults
+      #
+      # We nuke the DB storage provider from site settings, so need to yank out the existing settings
+      #  and pretend they are default.
+      # There are a bunch of settings that are seeded, they must be loaded as defaults
+      SiteSetting.current.each do |k,v|
+        SiteSetting.defaults[k] = v
+      end
+
+      require_dependency 'site_settings/local_process_provider'
+      SiteSetting.provider = SiteSettings::LocalProcessProvider.new
+    end
+
+    class DiscourseMockRedis < MockRedis
+      def without_namespace
+        self
+      end
+
+      def delete_prefixed(prefix)
+        keys("#{prefix}*").each { |k| del(k) }
+      end
+    end
+
+    config.before :each do |x|
+      # TODO not sure about this, we could use a mock redis implementation here:
+      #   this gives us really clean "flush" semantics, howere the side-effect is that
+      #   we are no longer using a clean redis implementation, a preferable solution may
+      #   be simply flushing before tests, trouble is that redis may be reused with dev
+      #   so that would mean the dev would act weird
+      #
+      #   perf benefit seems low (shaves 20 secs off a 4 minute test suite)
+      #
+      # $redis = DiscourseMockRedis.new
+      #
+      # disable all observers, enable as needed during specs
+      #
+      ActiveRecord::Base.observers.disable :all
+      SiteSetting.provider.all.each do |setting|
+        SiteSetting.remove_override!(setting.name)
+      end
+
+      # very expensive IO operations
+      SiteSetting.automatically_download_gravatars = false
+
+      Discourse.clear_readonly!
+
+      I18n.locale = :en
+    end
+
+    class TestCurrentUserProvider < Auth::DefaultCurrentUserProvider
+      def log_on_user(user,session,cookies)
+        session[:current_user_id] = user.id
+        super
+      end
+
+      def log_off_user(session,cookies)
+        session[:current_user_id] = nil
+        super
+      end
+    end
+
+  end
+
+  def freeze_time(now=Time.now)
+    datetime = DateTime.parse(now.to_s)
+    time = Time.parse(now.to_s)
+
+    DateTime.stubs(:now).returns(datetime)
+    Time.stubs(:now).returns(time)
+  end
+
+  def file_from_fixtures(filename)
+    FileUtils.mkdir_p("#{Rails.root}/tmp/spec") unless Dir.exists?("#{Rails.root}/tmp/spec")
+    FileUtils.cp("#{Rails.root}/spec/fixtures/images/#{filename}", "#{Rails.root}/tmp/spec/#{filename}")
+    File.new("#{Rails.root}/tmp/spec/#{filename}")
+  end
+end
+
+Spork.each_run do
+  # This code will be run each time you run your specs.
+  Discourse.after_fork
+end
+
+# --- Instructions ---
+# Sort the contents of this file into a Spork.prefork and a Spork.each_run
+# block.
+#
+# The Spork.prefork block is run only once when the spork server is started.
+# You typically want to place most of your (slow) initializer code in here, in
+# particular, require'ing any 3rd-party gems that you don't normally modify
+# during development.
+#
+# The Spork.each_run block is run each time you run your specs.  In case you
+# need to load files that tend to change during development, require them here.
+# With Rails, your application modules are loaded automatically, so sometimes
+# this block can remain empty.
+#
+# Note: You can modify files loaded *from* the Spork.each_run block without
+# restarting the spork server.  However, this file itself will not be reloaded,
+# so if you change any of the code inside the each_run block, you still need to
+# restart the server.  In general, if you have non-trivial code in this file,
+# it's advisable to move it into a separate file so you can easily edit it
+# without restarting spork.  (For example, with RSpec, you could move
+# non-trivial code into a file spec/support/my_helper.rb, making sure that the
+# spec/support/* files are require'd from inside the each_run block.)
+#
+# Any code that is left outside the two blocks will be run during preforking
+# *and* during each_run -- that's probably not what you want.
+#
+# These instructions should self-destruct in 10 seconds.  If they don't, feel
+# free to delete them.