[tests] Don't import QUnitTestCase into tests' global namespace Unittest's test loader will try to execute QUnitTestCase's test_javascripts method. However this class is intended to be subclassed, not to be executed directly. This change has the following consequences: * slightly faster test execution * almost all rtags warnings are gone

missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/*/cubicweb/skeleton/debian/rules.tmpl)