Add test for install of pyqpbo library, modify .travis.yml to fix path
problems in finding installed pyqpbo library
Merge pull request #19 from fgregg/master

Begining of test for installation of inference methods
TST before running the switch_to ad3 test, test that ad3 is actually installed.
point to andrea's pyqpbo repo in requirements
Merge pull request #21 from fgregg/patch-1

point to andrea's pyqpbo repo in requirements
Merge branch 'master' of github.com:pystruct/pystruct into adding-ad3