Split int/float division cases for efficiency, make it work even if C compiler takes floor (don't know of any that do).

Throwing an error is to invasive for 0.11.x, and also one needs to be able to subclass/access attributes of builtin types before we get rid of the declaration altogether.

--HG--
rename : tests/bugs/missing_self_in_cpdef_method_T165.pyx => tests/errors/missing_self_in_cpdef_method_T165.pyx