What is the problem?
We have a need to disable pitchfork via the `RUN_PITCHFORK` env.
However, `RUN_PITCHFORK` is checked for existence/non-emptiness in both
`bin/rails` and `config/unicorn_launcher`. This means setting
`RUN_PITCHFORK=0` enables pitchfork, which is counterintuitive.
What is the solution?
Change the checks to explicitly test for the value `"1"`. Now only
`RUN_PITCHFORK=1` enables pitchfork, while `0` or unset uses unicorn.