Fix bug in string replace regexp with function when returning non-string.

test/mjsunit/string-replace.js

Index: test/mjsunit/string-replace.js
diff --git a/test/mjsunit/string-replace.js b/test/mjsunit/string-replace.js
index d72f73bc46e81cb325308d6ddb57d4c7978113c7..ea6912724399bd37d99cd1d72ab1a33576f29616 100644
--- a/test/mjsunit/string-replace.js
+++ b/test/mjsunit/string-replace.js
@@ -180,3 +180,11 @@ longstring = 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", /[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; });