Create a new libsubid

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>