Move code generation for storing to a reference out of the AST nodes, and

Move code generation for storing to a reference out of the AST nodes, and
onto the platform-specific Reference class defined in codegen-*.cc.  This
removes all of the static code generator functions.
Review URL: http://codereview.chromium.org/6527

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@460 ce2b1a6d-e550-0410-aec6-3dcde31c8c00