Add ChildProcessWorkingDirectory option on reload

Adds option to allow overriding the working directory for the child process that is forked on reload

This is useful if you don't want the initial working directory to persist across all reloads. For example if you use capistrano for deployment and only keep the last 5 release directories, you'll eventually end up in a state where the wd doesn't exist anymore, which will cause a panic because getwd will fail.

@snormore @jduff for review please, thanks!