Bug introduced in r4608 where Dup2 increses the frame height with 4 instead of 2 when in a spilled scope.

Also removed a bogus ASSERT and used Push from macro assemler for double pushes.

TBR=erik.corry@gmail.com
Review URL: http://codereview.chromium.org/2005005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4611 ce2b1a6d-e550-0410-aec6-3dcde31c8c00