Until the dust settles, this is better than manually patching Sage's Cython.

make IntNode smarter about the type of integer it chooses for its value, promote plain >=32bit literals to Python objects to make sure their values pass through the C code

Excludes buffers and C++, which have their own code.
This is in preparation for #591 (inline vs. cdivision) and
support for inline complex arithamtic.