Added private recursive_delete as alternative to DELETE_TREE

[duffyjp]

delete_tree checks if you LDAP server supports the DELETE_TREE control code and then either uses it, or recursively deletes instead-- to the same effect.

[duffyjp]

I tracked down the source code for "ldapdelete" and it looks like that always does a recursive delete, rather than using the control code. I see no reason not to use DELETE_TREE if it's available though.

https://opensource.apple.com/source/OpenLDAP/OpenLDAP-208.5/OpenLDAP/clients/tools/ldapdelete.c

Here's an interesting chunk. If you pass -r it does a recursive delete, if not it just tries to delete the entity and fails if it has children. Like ruby-net-ldap's delete.

    /* If prune is on, remove a whole subtree.  Delete the children of the
     * DN recursively, then the DN requested.
     */
    if ( prune ) {
retry:;
        deletechildren( ld, dn, subentries );
    }

    rc = ldap_delete_ext( ld, dn, NULL, NULL, &id );

[HarlemSquirrel]

This looks great! Would you be able to write a test for this?

[HarlemSquirrel]

I've got a test for this ready. It looks like OpenLDAP doesn't support the delete tree control and we didn't have a test for this.