Remove unneeded ToString calls. We call ToString if necessary...

src/string.js

Index: src/string.js
===================================================================
--- src/string.js	(revision 2352)
+++ src/string.js	(working copy)
@@ -433,7 +433,7 @@
   if (m == 1) {
     var s = CaptureString(subject, lastMatchInfo, 0);
     // Don't call directly to avoid exposing the built-in global object.
-    return ToString(replace.call(null, s, index, subject));
+    return replace.call(null, s, index, subject);
   }
   var parameters = $Array(m + 2);
   for (var j = 0; j < m; j++) {
@@ -441,7 +441,7 @@
   }
   parameters[j] = index;
   parameters[j + 1] = subject;
-  return ToString(replace.apply(null, parameters));
+  return replace.apply(null, parameters);
 }