Setup "pgid" for server running in foreground mode

[kradima]

It's expected that pgid to be setup for "foreground" running server rather than for "background".

So it should be changed to set_pgid if foreground?

See discussion https://github.com/rails/spring/commit/e16e085e4e6aada8b32198e98e0c8ae1ab7b9963#r18804964

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[grosser]

@jonleighton @develop7 @hjwylde plz review

[hjwylde]

LGTM

[develop7]

:shipit:

[jonleighton]

My memory of the spring code is not super fresh, but I think the code is correct as-is and this should not be merged.

The idea of the set_pgid method is that it ties the background spring process to the current terminal session. Therefore, when the terminal session ends, the background process also gets killed.

So I think merging this will result in orphaned spring processes accumulating on users' machines.

When running in 'foreground mode', the spring process is never detached. Therefore it will just be up to the parent process to kill it when necessary.

If people want to run spring outside of a terminal session, they should do so using spring server, then they can manage the starting/stopping manually as desired.