This change adds the option to peel off the first iteration of inner loops.

Loop peeling is off by default and can enabled by a flag. It also requires building a flow graph.

As part of this I added the possibility to clone AST nodes.

Review URL: http://codereview.chromium.org/998001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4205 ce2b1a6d-e550-0410-aec6-3dcde31c8c00