merge pyflakes-setup.py-2709.  Fixes Pyflakes' setup.py.  author: moe, reviewer: mithrandi.  closes #2709
merge pyflakes-setup.py-2709.  Fixes Pyflakes' setup.py.  author: moe, reviewer: mithrandi.  closes #2709

PyCQA/pyflakes,timothycrosley/frosted,saper/main-pyflakes,timothycrosley/frosted,epsy/pyflakes,pyflakes/pyflakes,bitglue/pyflakes,jayvdb/pyflakes,mattcaldwell/frosted,hugovk/frosted,janusnic/main-pyflakes,hugovk/frosted,timothycrosley/frosted_original_fork,asmeurer/pyflakes,nikolas/pyflakes