Compatibility for Python 2.6.
deb: fix some lintian warnings
skip a test on old lxml
higher tolerance for some image tests
higher relative tolerance for matplotlib (see http://tests.obspy.org/13879/#1)
deb packaging: adding python-tornado to dependencies.

on new ubuntu 14.04 trusty tahr obspy doesnt run (pkg_resources
complains about missing matplotlib dependency) if python-tornado is
not installed (used by matplotlib but not declared as dependency).
seishub tests: massive speedup if test server unreachable
seishub tests: move skipping to TestCase level
Merge branch 'releases'