tdb: suppress record write locks when allrecord lock is taken.

tdb: suppress record write locks when allrecord lock is taken.

Records themselves get (read) locked by the traversal code against delete.
Interestingly, this locking isn't done when the allrecord lock has been
taken, though the allrecord lock until recently didn't cover the actual
records (it now goes to end of file).

The write record lock, grabbed by the delete code, is not suppressed
by the allrecord lock.  This is now bad: it causes us to punch a hole
in the allrecord lock when we release the write record lock.  Make this
consistent: *no* record locks of any kind when the allrecord lock is
taken.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>