This eliminates a bunch of new errors for RPCs like SRUN_JOB_COMPLETE
which can fail if the srun has already terminated before the 
messages gets sent from slurmctld.

Rely upon slurmd and srun to tell us of the step's completion.

functionality.

There is a test for slaunch signal handling though.

use xstrcat() function rather than equivalent in-line code.

env_array_merge.

added --enable-bluegene-emulation mode and fixed it so sview won't build on systems that don't have gtk installed.

Default behaviour is to print a message notifying the user.  Also added
the -K/--kill-command option, which tells salloc to send a signal to the
user's command when a job-complete message arrives.