Make unknown pushrule conditions not match

Unknown conditions previously were assumed to match, but given rules
can be added on the server as base rules, it's probably better to not
match unknown conditions.

src/pushprocessor.js

@@ -1,5 +1,6 @@
 /*
 Copyright 2015, 2016 OpenMarket Ltd
+Copyright 2017 New Vector Ltd
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -126,7 +127,10 @@ function PushProcessor(client) {
         if (condition_functions[cond.kind]) {
             return condition_functions[cond.kind](cond, ev);
         }
-        return true;
+        // unknown conditions: we previously matched all unknown conditions,
+        // but given that rules can be added to the base rules on a server,
+        // it's probably better to not match unknown conditions.
+        return false;
     };
 
     const eventFulfillsRoomMemberCountCondition = function(cond, ev) {