Compatibility and Test Fixes from @Takbal

[tedsteiner]

@takbal I really appreciate all the effort you put into #79. I'm using this pull request to track my progress as I work through understanding the changes you made.

[tedsteiner]

The compatibility changes in this commit from @takbal allowed the tests to pass for me on both OS X El Capitan and Ubuntu 14.04.

Like @takbal mentioned, I also saw that the plots.jl tests took significantly longer with Julia 0.4.2 than they ever did previously, probably because it has over 3.8 GB of memory allocations for some reason. My guess is that this is internal to Winston.jl rather than this package, which is unfortunate but something we'll probably just have to deal with.

I'm pretty sure that the test failures on Travis are due to LibExpat.jl issues rather than related to this package. I still don't know what to do about this, but no machine I've ever tested on has ever reproduced this problem with LibExpat.jl, so I believe it to be Travis-specific.