Update matplotlib to version 1.3.1.

I added a licence field as discussed in
https://groups.google.com/forum/#!topic/hashdist/aJQkqm9hZZw
Sort travis test cases alphabetically.
Separate out testcase for matplotlib.
add verify functionality to matplotlib build
Merge pull request #1 from hashdist/ahmadia/add_matplotlib_travis

add verify functionality to matplotlib build
Don't delete pth files after install.

pth files are required for namespace packages.
Merge pull request #213 from lanewittgen/master

Update matplotlib to version 1.3.1.