BUG/VIS: correctly test for yaxis ticklocs across different versions of MPL
closes #4789

i'm going to add a wheel for mpl 1.3 on travis...will run on the py27 "not slow" job

@jreback @y-p any objections to that?
 sounds good
 actually it has to run on the "slow" build
 i tried this with matplotlib 1.1.1, 1.2.0, 1.2.1, and 1.3.0 locally and tests pass so if there aren't any other objections... going to merge in a bit
 we only have 1 plot build? or 2?
 just 1 bc of the slow dec....there are a few plotting tests that aren't marked  slow
 ok 2 merge?
 do we have another plot build? (or just the one)?
 oh...sorry. ou answered that....add another of the builds?
 actually its ok...nvm
