Simplify Python version checks, fix a bug

[hugovk]

The one in psutil/tests/__main__.py looks like an unintentional bug:

if sys.version_info[:2] == (2, 6):
    TEST_DEPS.extend(["ipaddress", "unittest2", "argparse", "mock==1.0.1"])
elif sys.version_info[:2] == (2, 7) or sys.version_info[:2] <= (3, 2):
    TEST_DEPS.extend(["ipaddress", "mock"])

That second elif is also true for Python 2.6 because or sys.version_info[:2] <= (3, 2) is always true.

Python 2.6 then has both mock==1.0.1 and mock in TEST_DEPS.

[giampaolo]

setup.py just changed and this is no longer necessary. Thanks though.