Check Python version rather than System version.

[wtpayne]

The intent of the _IS_PYTHON_3 test appears to be to check the version of the Python interpreter not the version of the system.

If this is the case, then a call to platform.python_version() is required rather than platform.version(), as per the docs.

(platform.version() returns the system's release version, whereas platform.python_version returns the python version)

https://docs.python.org/2.6/library/platform.html?highlight=platform#platform.version https://docs.python.org/2.7/library/platform.html?highlight=platform#platform.version file:///usr/share/doc/python3-doc/html/library/platform.html?highlight=platform#platform.version