* py-matplotlib only needs backports when ^python@:2
This implements @scheibelp's suggestion in #13711.
py-matplotlib should only depends_on py-backports-functools-lru-cache
when it's using a python that actually *needs* it.
See #13711 for details.
* Don't depend_ons py-enum34 unless python@:3.3
* Tighten up enum34 dependency
@adamjstewart cracked open the setup.py files and suggested a tighter
dependency for py-enum34. 1.4 and 1.5 only require it for pythons
before 3.4, 1.3 requires it unconditionally. So...., we'll do the
same.
* Remove conflict on python 3.4 from enum34
at @adamjstewart's request see PR notes
7a6c7f23a0