ldb: Attach appropriate ldb context to returned result

ldb: Attach appropriate ldb context to returned result

This is done by adding a new API that avoids the problems of
ldb_dn_copy() and makes it clear that a struct ldb_context *
pointer will be stored in the new copy.

Signed-off-by: Jo Sutton <josutton@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>