r13786: [merge] Add registration functions for LDB modules

r13786: [merge] Add registration functions for LDB modules

Applications that use LDB modules will now have to run ldb_global_init()
before they can use LDB.

The next step will be adding support for loading LDB modules from .so
files. This will also allow us to use one LDB without difference between the
standalone and the Samba-specific build
(This used to be commit 52a235650514039bf8ffee99a784bbc1b6ae6b92)