replaced local gtk m4 test with AM_PATH_GTK_2_0 also changed AC_CHECK_LIB to AC_SEARCH_LIBS to avoid extra libs in compile lines.

moved socket_accept and socket_readable functions into a common place for all the calls since the code was very similar.

   in sattach.c, step_launch.c, and allocate_msg.c

job_desc_msg_t - in, out, err have been changed to std_in, std_out, and std_err respectfully.  Needed for PySLURM, since Python sees (in) as a keyword.

1. sfree and scontrol now free blocks.
2. correct connection type is given for jobs now.
3. configuring jobs are set at the correct time now

plugin_load_from_file(). Be sure to collect this error and
return a useful error message to the slurm log.

Additionally, even though I don't think plugin refcounts actually
do anything in SLURM, the refcount was inadvertently incremented
on PLUGIN_INVALID_HANDLE instead of for valid handles. This patch
fixes that bug as well.
(From Mark Grondona)