[Caja] substr fix in IE<9 (issue 5489043)

[felix8a]

Reviewers: metaweta,

Description:
I forgot that in IE<9, s.substr(-1) === s.substr(0)
Please review this at http://codereview.appspot.com/5489043/

Affected files:
  M     src/com/google/caja/es53.js


Index: src/com/google/caja/es53.js
===================================================================
--- src/com/google/caja/es53.js (revision 4683)
+++ src/com/google/caja/es53.js (working copy)
@@ -247,7 +247,7 @@
       var keys = fastOwnKeys(this);
       for (var k = 0, n = keys.length; k < n; k++) {
         var i = keys[k];
-        if (i.substr(-5) !== '_v___' || i.length < 6) { continue; }
+        if (i.length <= 5 || i.substr(i.length - 5) !== '_v___') {  
continue; }
         var P = i.substr(0, i.length - 5);
         this[P + '_c___'] = false;
         this[P + '_gw___'] = false;