PyRun_FileEx().  These are the same as their non-Ex counterparts but
have an extra argument, a flag telling them to close the file when
done.

Then this is used by Py_Main() and execfile() to close the file after
it is parsed but before it is executed.

Adding APIs seems strange given the feature freeze but it's the only
way I see to close the bug report without incompatible changes.

[ Bug #110616 ] source file stays open after parsing is done (PR#209)