r16774: This patch modifies the tdb API to allow the logging function to be used

r16774: This patch modifies the tdb API to allow the logging function to be used
as part of ldb.

This allows tdb failures to be passed all the way up to Samba's DEBUG
system, which allowed easier debugging.

Unfortunately I had to extend the tdb API, as the logging function
didn't have a context pointer.

I've worked over the 'debug levels' in TDB.  Most of them were 0,
which didn't seem right, as some were trace-like messages.  We didn't
see any of these previously, except when accessing TDB directly.

Andrew Bartlett
(This used to be commit 58898092c1ce043f6d698db5065f372b79109e22)