while adding functions and other properties.  This gives around 2% on
context-create, more if we don't GC on every new context.  Also fix
accounting bug in cell space.
Review URL: http://codereview.chromium.org/165449

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2681 ce2b1a6d-e550-0410-aec6-3dcde31c8c00