fix craches where session pgid is unknown #330

[oklas]

This changes make it possible to work on some os.
It contains only pgid result checking and catch exceptions if any.

(more about problem in discussion #330)

[rails-bot]

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[oklas]

@rafaelfranca this does not broke tests and does not add new feature - this is only fix. Can you please comment or request anything to step to merge?

[oklas]

Happy new year!

[oklas]

Hi @rafaelfranca

This changes actually contains only checking and catch exceptions to make it worked on some os.

Could you review and merge?

[rafaelfranca]

Can you confirm this is still a problem with newest release of spring?

[oklas]

I can not even confirm problem with one of previous release 2.1.0 - seems it is worked (it can start and stop without crash). It is strange but I think there is no sense to spend time to inspect. The problem was on Freebsd partially because ps does not support -o sess=. Current version seems does not use such ps output. But I notice another minor problem and submit it here #660.