we can DND a contact on another account's group if we are in merged mode. Fixes #1888

src/roster_window.py

@@ -3132,6 +3132,10 @@ _('If "%s" accepts this request you will know his or her status.') % jid)
 			return
 		source_account = model[iter_source][C_ACCOUNT].decode('utf-8')
 		if account != source_account:	# dropped in another account
+			if self.regroup and type_dest == 'group':
+				# on a group in merge mode is ok
+				account = source_account
+			else:
 				return
 		it = iter_source
 		while model[it][C_TYPE] == 'contact':