Added further integrity checking, this time checking for duplicate directory

Added further integrity checking, this time checking for duplicate directory
entries and for orphaned nodes in the database.

Added two flags, -R and -L, to disable the recovery code and the remove of
/local at start-up.  This makes it much easier to analyse corrupted tdb files.

Added some missing talloc_free calls in the previous integrity checking code.

Removed the transaction handle from the trace_io message -- unfortunately,
the transaction is always null at this point, as it's not yet been looked up.

Signed-off-by: Ewan Mellor <ewan@xensource.com>