ldb: Release ldb 1.4.0

ldb: Release ldb 1.4.0

* New LMDB backend (experimental)
* Comprehensive tests for index behaviour
* Enforce transactions for writes
* Enforce read lock use for all reads
* Fix memory leak in paged_results module.
  We hold at most 10 outstanding paged result cookies
  (bug #13362)
* Fix compiler warnings
* Python3 improvements
* Restore --disable-python build
* Fix for performance regression on one-level searches
  (bug #13448)
* Samba's subtree_rename could fail to rename some entries
  (bug #13452)

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>