Handle unsupported version at runtime.
Handle unsupported version at runtime.

If you have an ancient setuptools, 4a36ddb3aa77b8d1b1a64c197607fa652705856c
won't successfully prevent installing. These changes will at least give a sane error,
rather then  just barfing on random syntax errors due to the `unicode` type not
being present in py3k.

Cherry picked from 2f20f2d

foosel/OctoPrint,Jaesin/OctoPrint,Jaesin/OctoPrint,Jaesin/OctoPrint,foosel/OctoPrint,Jaesin/OctoPrint,foosel/OctoPrint,foosel/OctoPrint