It looks like the tk backend is broken with 1.5.3 and 2.0.0 on windows, most likely following #6442

To reproduce:

1. install python 2.7.12 x64 windows from python.org, and wheels gholke for 2.7
2. do python -c "import matplotlib.backends._tkagg", which fails:

>>> import matplotlib.backends._tkagg
...
RuntimeError: Could not find TCL routines

I have seen the same issue with:

• our own build of 1.5.3 in canopy (for 2.7)
• in Gholke wheels for 1.5.3 and 2.0.0 (2.7.12)
• conda package as well for 1.5.3 (both 2.7.13 and 3.5.2)