warnings.showwarning() was being used. This broke pre-existing replacements for
the function since they didn't support the extra argument.
Closes issue 2705.
'warnings' code in places where it was previously not possible (e.g., the
parser). It could also potentially lead to a speed-up in interpreter start-up
if the C version of the code (_warnings) is imported over the use of the
Python version in key places.
Closes issue #1631171.