Currently we only pass a boolean parameter indicating whether
the input operands to the GenericBinaryOpStub are guaranteed
to be numbers or not. 

Instead we pass the complete number type as a parameters. This 
allows to use more precise type information for code generation
in the stub.

Also make the computation of the result type more precise and correct on both ia32 and x64.

Review URL: http://codereview.chromium.org/593110

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3873 ce2b1a6d-e550-0410-aec6-3dcde31c8c00