Add a bit of bulletproofing.

Add a bit of bulletproofing.

When a drone finishes servicing a request, it writes a brief message
to a pipe, to notify the listener that it's available for another request.

Change: if the write to the pipe is not successful, log an error message
and terminate.  Otherwise the drone would become undead and unreachable.

M    src/libopensrf/osrf_prefork.c

git-svn-id: svn://svn.open-ils.org/OpenSRF/trunk@1968 9efc2488-bf62-4759-914b-345cdb29e865