modular.

This makes it simpler to enable detailed debugging for reservations.
This includes more information than we probably want to see with
the DebugFlag=reservation and would be only for developer debugging

This might have worked fine for core reservations or when there
are sufficient idle nodes to use, the the select_g_resv_test()
function clears the node bitmap for nodes that it can not use
and the reservation create logic did not restore that bitmap
after a failed resource selection attempt. This logic restores
the node bitmap on a failed call to select_g_resv_test() so we
can add nodes to the bitmap of available nodes rather than having
it repeatedly cleared.
The logic also adds some performance enhancements that I will
add to in the next commit.

This fixes a bug where a system is enforcing memory limits and
the job already has a step running on some of the nodes then
tries to start another step using some of those nodes. For example
wwith DefMemPerNode configured and the select plugin enforcing
memory limits, try:
salloc -N2 bash
$ srun -N1 sleep 10&
$ srun -N2 hostname
Without this patch, the second srun would fail instead of pend.

on a task level if any task hit it the check will be triggered)

Conflicts:
	doc/man/man5/cgroup.conf.5
	src/plugins/task/cgroup/task_cgroup_memory.c

use mem and memsw failcnt, check for existence

Thanks Ryan.  I'll let you know how it goes.

info about cgroups on Debian, et al

environment.