[docs] [issue26095] Update porting HOWTO to special-case Python 2 code, not Python 3

[Nick Coghlan]

Nick Coghlan added the comment:

The feature detection approach is especially important for anything covered by the security backports in PEP 466 and 476, but can also apply for things like installing the importlib2 meta_path hooks into Python 2.7.

----------
nosy: +ncoghlan

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue26095>
_______________________________________