Run tests more verbosely

--HG--
extra : amend_source : 58fa4b9ba5b06708db12a99d87c5c9041ffdb622
Make it possible to run tests without 'matplotlib' installation
Run tests also on Python 2.6
Use several numpy/scipy pairs for testing
Fix test failure on Python 2.6/numpy 1.6.1/scipy 0.9.0