interface statistics, have its error messages come out as sync-pipe
errors, have it send a sync-pipe "success" message on success, and have
the callers get that message and display it.
svn path=/trunk/; revision=32843
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.
svn path=/trunk/; revision=17789