function.func_code.co_names has all the names used in the function, including name of attributes. It will pickle some unnecessary globals if there is a global having the same name with attribute (in co_names).

There is a regression introduced by #2144, revert part of changes in that PR.

cc JoshRosen

Author: Davies Liu <davies.liu@gmail.com>

Closes #2522 from davies/globals and squashes the following commits:

dfbccf5 [Davies Liu] fix bug while pickle globals of function