ESLURM_TASKDIST_REQUIRES_OVERCOMMIT.

Fix but in new env.c code.

variables.
It can also support a VERY limitted overcommit.  It only works if you
are using all nodes in the allocation.  Need to make this work for a subset.

as "localhost". Don't report errors when actual hostname is not found 
in node list.

Code is still in development; it is compteley #ifdef'ed out.

Move slurm_step_layout_t struct to slurm.h.in so we can use it as the
returned object of a future API function.

altered the resource allocation and job_step_create_response structures.  Also altered the step_layout structure