Unicorn pre-forks workers upfront. New processes are not created per request. posix-spawn is also only useful for fork+exec, where the new process starts execu

Unicorn pre-forks workers upfront. New processes are not created per request. posix-spawn is also only useful for fork+exec, where the new process starts executing a new binary. This is not the case in unicorn or resque, where the child processes actually need to be copies of the parent. We're currently using posix-spawn in albino and grit, which execute external commands like `pygmentize` and `git`