TRQ-2176. Make it so that if mother superior gets an abort from a pbs_mom telling it to that the job can't run that it doesn't send an abort back to that exact same mom.
Change the name and return of check_ms() to be clearer. The function is now connection_from_ms() and false means it isn't from the mother superior while true means it is. It also returns a boolean value now.
TRQ-2180. Fix a crash when cleaning up a job if the exec hosts are NULL.
Make some cleanup changes to my fixes for TRQ-2176.