Loop peeling for inner loops.

Loop peeling for inner loops.

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