Don't require enum34 in python >= 3.4
Don't require enum34 in python >= 3.4

This fixes the build in distros which no longer provide python3-enum34.

pythongssapi/python-gssapi,pythongssapi/python-gssapi,frozencemetery/python-gssapi,frozencemetery/python-gssapi,frozencemetery/python-gssapi,pythongssapi/python-gssapi