r10753: don't require every ldb module to implement both a search_bytree() and

r10753: don't require every ldb module to implement both a search_bytree() and
a search() function, instead each module now only implements the
bytree method, and the expression based search is handled generically
by the modules code. This makes for more consistency and less code
duplication.

fixed the tdb backend to handle BASE searches much more
efficiently. They now always only lookup one record, regardless of the
search expression