This should decrease the number of realloc calls and 
improve performance.

Update slaunch man page.
Add beginnings of salloc man page.

Handles SRUN_PING most importantly, but also has stubs for 
SRUN_TIMEOUT and SRUN_NODE_FAIL.  The latter two print messages,
but do not take any action.

"resp_port" and "io_port".  Now they just list the available listening
ports in the client (srun/slaunch), instead of listing a port per node
(which contains many duplicate ports).  The slurmd picks a port to use
based on number of available ports modulo its own rank in the job step.

- SlurmdPidFile, SlurmdLogFile, and SlurmdSpoolDir may each contain a
  "%h" and/or a "%n", which will be replaced by the hostname or NodeName,
  respectively.
- Add new xstring.c xstrsubstitute() function.
- launch_tasks_response_msg_t structure now contains a task_ids array
- Remove SLURM_DIST_UNKNOWN from enum task_dist_states
- job_desc_msg_t now lists a seperate addresses for the 
  RESPONSE_RESOURCE_ALLOCATION message.
- Expand the job step context concept used previously for task "spawn"
  for poe.  The step context is now also used for nomal step launch.
  New SLURM API function slurm_step_launch() and associated support
  functions.
- Fix spaghetti header #includes relating to global_srun.[ch]
- Fix slurmctld segfault when slaunch --relative is used

close on the file descriptor.