task distribution (but may fail if switch does not support arbitrary).

poe may have problems with the spawn_task changes.

  Add -D, --dependency option
  Man page updates.

removed task dist from srun put into slurmctld.  need to remove the addresses from job allocation since that isn't needed anymore.  need to fix some issues with the way sbcast does things now which should be easy.  The switch plugins can change also since we have the tasks laid out already now before we set up the switch.  Some more clean up also will be nice in srun.

  - returns the return code of its child command
  - add timeout for limiting how long it waits for a PENDING job allocation
    (slurm_allocate_resources_blocking was updated to timeout correctly)
  - cleans up job allocation on Ctrl-C (Actually, it ignores SIGINT, SIGTERM,
    SIGQUIT, but unblocks them for the child, so ctrl-c from the shell
    hits the whole process group, and the child exits, and salloc cleans
    up like normal.  Might to be more proactive with signals, but I
    am not yet certain.)
  - trim more unnecessary command line options
  - man page additions

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.