* Scope limitations now have their own section, rather than being
part of the Rationale section
* reordered backport sections so PEP 493 backport is discussed
prior to the PEP 476 backport
* made it explicit that the PEP 476 section is aimed at "*IF* you
backport this feature, do it *this* way", so simply not implementing
that section at all is entirely PEP compliant
- now has 2 feature sections, and 3 backport recommendations
- features are for a new Python API and environment setting
- backports are all for targeting versions < 2.7.9
- Python 3 is excluded from scope
* Describe the fallback in the absence of the PEP
* Check sys.flags.ignore_environment in sample code
* Explicitly limit backport scope to Linux distros
* Explicitly cover (lack of) interaction with virtualenv