Implement flag and source getters on RegExp.prototype.

test/webkit/fast/regex/toString-expected.txt

Index: test/webkit/fast/regex/toString-expected.txt
diff --git a/test/webkit/fast/regex/toString-expected.txt b/test/webkit/fast/regex/toString-expected.txt
index 3e661dd879de41a05034ddbdaf644280ac21922d..65e88ebd392f1c37e761a3ad575d706f9f414742 100644
--- a/test/webkit/fast/regex/toString-expected.txt
+++ b/test/webkit/fast/regex/toString-expected.txt
@@ -28,7 +28,7 @@ On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE
 
 PASS RegExp('/').source is "\\/"
 PASS RegExp('').source is "(?:)"
-FAIL RegExp.prototype.source should be (?:) (of type string). Was undefined (of type undefined).
+FAIL RegExp.prototype.source should be (?:). Threw exception TypeError: RegExp.prototype.source getter called on non-RegExp object
 PASS RegExp('/').toString() is "/\\//"
 PASS RegExp('').toString() is "/(?:)/"
 FAIL RegExp.prototype.toString() should be /(?:)/. Threw exception TypeError: Method RegExp.prototype.toString called on incompatible receiver [object Object]
@@ -58,3 +58,4 @@ PASS successfullyParsed is true
 
 TEST COMPLETE
 
+