Also fix a potential bug with self.to_py_function beign assigned to soon.

--HG--
extra : transplant_source : %279%83%AB%FF%04%F0%F6%12%BB%D1P%19%A9%B9%F2%C6%C23%B6

--HG--
extra : transplant_source : %DA%97_%C9%8A%9E%ED%3F7%FC4m%1E%E6%0E%D3%89l%DF%D4

seems that allowing C functions without argument names to coerce to Python functions goes wrong (note: Python coercion is attempted more often than needed!)

reuse existing types/names in module for cfunc wrapping instead of redeclaring them in the utility code

--HG--
extra : transplant_source : %D31l%C2%F1BM%00%92l1%99%C0l%E8e%FC%9C%0C%AA

--HG--
extra : transplant_source : %B2a%A7%A9%A6%2A%2C%21%11%A1%D3%A0%F4%0D%D1%C7K%97%60_

--HG--
extra : transplant_source : %A4%C2%DA%5EV%1C%17%07%E3%E9%9E%C7%AB%1EF%2C%C8%A7%1C%5D

--HG--
extra : transplant_source : 7P%DF%9E%F8%A3%2B%98%17V%CB%9E%EC%A3m%28G%1Bv%A1

--HG--
extra : transplant_source : %10%00%9D%98%A4O%02%1A%ACs%3F%92gB%E2%21%7B%1Eo%C8

--HG--
extra : transplant_source : s%10%909%A0X%06O%D6A%C6%DEEUM%80%15%3D%C7%83

make cfunc wrapper function support kwargs if the defining module wants it and give it a docstring that shows the argument names