CLN: move assignment from header into cython
an insignificant refactoring that allows PyPy2.7  to build and import Pandas. The original code uses functions that are macros in CPython but actual c-functions in PyPy and one cannot assign to a function result

Note that while PyPy imports Pandas, it very quickly segfaults, Apparently PyPy does not yet play well with enough of Cython, I suspect strange interactions with tp_new and tp_deallocate