two words: there is no reason to keep a pointer to the current code
generator and macro assembler in the JumpTarget.
Review URL: http://codereview.chromium.org/113458

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1987 ce2b1a6d-e550-0410-aec6-3dcde31c8c00