Some const correctness. Stop tdb being used as a remote backend. If an

Some const correctness. Stop tdb being used as a remote backend. If an
idmap backend is specified cause smbd to ask winbindd (use winbindd if
you want a consistant remote backend solution).
Should work well enough for next beta now...
Jeremy.
(This used to be commit 8f830c509af5976d988a30f0b0aee4ec61dd97a3)