The script mirror is now created through MakeMirror like all other mirrors preserving handle identity. Added a couple of properties to the script mirror and added some more tests for the script mirror.
Review URL: http://codereview.chromium.org/21074

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1227 ce2b1a6d-e550-0410-aec6-3dcde31c8c00