In Python 3.x, internal_close() returns -1 on error (if close() 
returns a negative value) and 0 on success.

In Python 2.x, internal_closes() returns the errno value of close() on 
error, or 0 on success. fileio_close() tests if the error value is 
negative instead of if it's not null or at least it's strict positive.

Python 3.x code looks better. I tried to backport the internal_close() 
changes but I get a segfault on PyErr_WriteUnraisable() :-p (close() 
error in fileio_dealloc)