tg.sh: improve needs_update_check remote base handling
Ignore the refs/remotes/... dependency line generated by recurse_deps
and check the remote base at the same time and handle the result the
same way the remote head is handled.
This makes use of needs_update_check_no_same(self) work more sanely.
Otherwise a remote base that's ahead triggers a "behind" for the
branch while a remote head that's ahead does not and that's just wrong.
The tg summary display should now be copacetic (even more so than it's
ever been before).
Signed-off-by: Kyle J. McKay <mackyle@gmail.com>