Fix bug in string replace with nonparticipating captures.

test/mjsunit/string-replace.js

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 160 matching lines @@
 longstring = longstring + longstring;
 longstring = longstring + longstring;
 longstring = longstring + longstring;
 longstring = longstring + longstring;
 longstring = longstring + longstring;
 longstring = longstring + longstring;
 longstring = longstring + longstring;
 longstring = longstring + longstring;
 // longstring.length == 5 << 11
 
-replaceTest(longstring + longstring, 
+replaceTest(longstring + longstring,
             "<" + longstring + ">", /<(.*)>/g, "$1$1");
-            
+
 replaceTest("string 42", "string x", /x/g, function() { return 42; });
-replaceTest("string 42", "string x", /x/, function() { return 42; });            
+replaceTest("string 42", "string x", /x/, function() { return 42; });
 replaceTest("string 42", "string x", /[xy]/g, function() { return 42; });
 replaceTest("string 42", "string x", /[xy]/, function() { return 42; });
 replaceTest("string true", "string x", /x/g, function() { return true; });
 replaceTest("string null", "string x", /x/g, function() { return null; });
-replaceTest("string undefined", "string x", /x/g, function() { return undefined; });            
+replaceTest("string undefined", "string x", /x/g, function() { return undefined; });
+
+replaceTest("aundefinedbundefinedcundefined", 
+            "abc", /(.)|(.)/g, function(m, m1, m2, i, s) { return m1+m2; });