o common/eio.c : add close handler to io objects, call close handler

   on POLLHUP but no read method.
 o common/log.c : add pthread_atfork() calls to ensure sanity of log
   data structure after a fork() from a threaded program.
 o slurmd/io.c : set _obj_close as close handler for all objects
 o slurmd/shm.c : fix bug that caused lockfile to always go into /tmp
 o slurmd/mgr.c : reset log prefix to denote job id when logging to a file
 o srun/srun.c : do not call fatal() after having allocated nodes,
   use die() instead which prints an error then does goto cleanup;
 o srun/*.c : remove _debug vestigal var