messaging4: Use messages_dgm

messaging4: Use messages_dgm

This replaces the transport mechanism in source4 with calls to the
messages_dgm code. It is supposed to enable "smbcontrol samba pool-usage"
as an example without having to rewrite smbcontrol using the source4
based messaging subsystem.

This moves the source3 based names.tdb (which is unused so far) to the
lock directory, source4 does not have a cache directory.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>