that ip can be used as a scratch register. This is not true because
ip is already used for something else in AllocateInNewSpace in the
macro assembler.

Explicitly allocate a temp register for use in the heap number
allocation instead.
Review URL: http://codereview.chromium.org/5788001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5967 ce2b1a6d-e550-0410-aec6-3dcde31c8c00