Continuing the linux / proc PMDA split.

Continuing the linux / proc PMDA split.

- fix the proc instance domain table initialization - it's sparse
and preserves Linux indom numbers (for archive migration).

- move cgroup pmns root to CGROUP_ROOT ("proc.cgroup") and fix
a segfault in proc_dynamic_pmns(). "cgroup" can't be a top level
leaf node in the pmns file (would need other code changes to support
this, which we may want to consider).

- add linux_proc into the build (platform conditional) but not
enabled by default.

- trim code copied from ../linux/filesys.[ch] and #if 0 blocks.

- fix a bug in proc_fetchCallBack - wrong variable was being
returned for proc.cgroup.subsys.hierarchy

	modified:   src/pmdas/GNUmakefile
	modified:   src/pmdas/linux_proc/GNUmakefile
	modified:   src/pmdas/linux_proc/cgroups.c
	modified:   src/pmdas/linux_proc/cgroups.h
	modified:   src/pmdas/linux_proc/clusters.h
	modified:   src/pmdas/linux_proc/filesys.c
	modified:   src/pmdas/linux_proc/filesys.h
	modified:   src/pmdas/linux_proc/indom.h
	modified:   src/pmdas/linux_proc/pmda.c
	modified:   src/pmdas/linux_proc/pmns