BLD: run slow tests on new optional build 2.7_SLOW using current versions of everything
BLD: run graphics tests on 2.7_LOCALE using old matplotlib
TST: skip on < mpl 1.3.1 (GH8947)
Merge pull request #8949 from jreback/graphics

BLD/TST: skip mpl 1.2.1 tests (GH8947)