Create a new libsubid

Closes #154

Currently this has three functions: one which returns the
list of subuid ranges for a user, one returning the subgids,
and one which frees the ranges lists.

I might be mistaken about what -disable-man means;  some of
the code suggests it means just don't re-generate them, but
not totally ignore them.  But that doesn't seem to really work,
so let's just ignore man/ when -disable-man.

Remove --disable-shared.  I'm not sure why it was there, but it stems
from long, long ago, and I suspect it comes from some ancient
toolchain bug.

Create a tests/run_some, a shorter version of run_all.  I'll
slowly add tests to this as I verify they work, then I can
work on fixing the once which don't.

Also, don't touch man/ if not -enable-man.

Changelog:
	Apr 22: change the subid list api as recomended by Dan Walsh.
	Apr 23: implement get_subid_owner
	Apr 24: implement range add/release
	Apr 25: finish tests and rebase
	May 10: make @owner const

Signed-off-by: Serge Hallyn <serge@hallyn.com>

Makefile.am

@@ -2,5 +2,14 @@
 
 EXTRA_DIST = NEWS README TODO shadow.spec.in
 
-SUBDIRS = po man libmisc lib src \
-	contrib doc etc
+SUBDIRS = libmisc lib 
+
+if ENABLE_SUBIDS
+SUBDIRS += libsubid
+endif
+
+SUBDIRS += src po contrib doc etc
+
+if ENABLE_REGENERATE_MAN
+SUBDIRS += man
+endif