r8625: move the ldb_wrap logic into the ldb code. This logic is meant to

r8625: move the ldb_wrap logic into the ldb code. This logic is meant to
avoid the horrors of posix locking, but it was preventing us having an
ldb open twice with different options. Now each ldb open of the same
file shares the same underlying tdb, but uses a different ldb
structure
(This used to be commit 4e090c66dfa1d2764e4693578d3845be3b8893f6)