[issue28288] Expose environment variable for Py_Py3kWarningFlag

[Brett Cannon]

Changes by Brett Cannon <brett at python.org>:


----------
components: +Interpreter Core -2to3 (2.x to 3.x conversion tool)

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue28288>
_______________________________________