Make the cpus-per-proc equivalent a little more intuitive:

* allow users to specify just a modifier for map-by instead of requiring that they also specify a policy. Thus, we now accept --map-by :pe=3 as indicating that we should use the default mapping policy, but bind 3 cpus/proc.

* if users specify a pe's/proc but no policy, default to --map-by NUMA to ensure we have access to multiple cpus for the request. This won't guarantee we have access to enough to meet the request, but gives us a chance. In addition, we know that binding a proc to multiple cpus will work best if those cpus are all in the same NUMA, so this provides some degree of optimized behavior.

Per a request from Jeff, define "oversubscribe" for binding as a synonym for the "overload" modifier.

cmr=v1.8.2:reviewer=rhc