Unittests

A bunch of tests. refs #14

There are a lot of commits, and later ones overwrite previous ones. If you think that I should compact this — I will :)

I made my best to limit the tests strictly to the public APIs. I had to do some evil (monkey-patch style) mocking to disable network-calls, as urlllib is hardcoded into sparqlwrapper.

Tests should be run with `nosetests` or `nosetests --with-coverage --cover-html --cover-package=SPARQLWrapper`