Implemented continues integration with Travis-CI

I implemented continues integration with travis-ci. Take a look how it looks like in my fork (https://travis-ci.org/mmarkov/pygraphviz). 
Also added coveralls for code coverage ( take a look at https://coveralls.io/r/mmarkov/pygraphviz). 
I changed distutils with setup tools which is mainstream and feature rich. 
Also I had hard time finding so file because of local copy and virtual env, so I tried to improve a little bit module locator to handle even more cases than before.