Put the low-level sync routines into a common file so they can be shared

Put the low-level sync routines into a common file so they can be shared
by dumpcap and Ethereal (so that, on UN*X, the child process can report
a detailed "can't exec dumpcap" error).

Rename most of the "sync_pipe_XXX_to_parent()" routines, as they're also
in Tethereal, which doesn't have a sync pipe.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@17789 f5534014-38df-0310-8fa8-9805f1628bb7