pytest_00: initial py.test testing for tdi

[AvdN]

• run_tests filters out python files under tests/ that start with "test_"
• py.test (by default) only runs those files
• tox.ini file for creation of virtualenvs for testing
• initial conversion of 3 files (9 tests)
• test coverage based on py.test

Please note:

• tox needs to find Python2.5, 2.6 and 2.7 executables, it expects these in
  '/usr/bin', but there is a PR to allow explicit specification (my
  /usr/bin/python2.7 is 2.7.3 but with the patch I get my virtualenvs from
  /opt/python/x.y.z (2.7.5, 2.6.8, 2.5.6, etc.)
• tox keeps virtualenvs (under .tox) only first time the virtualenv is
  created needs installing (in addition I have a local PyPI cache, which
  speeds up the initial setup).
• added MANIFEST, ttake MANIFEST out of gitignore
• generated test_XX.py files for all files under tests
• there is a small helper file _test_support.py under tdi. It provides
  the mechanism to do both C and pure Python tests (and can
  easily be adapted to skip one of those for a particular Python version)
  (fixture 'pure', which adds pure python testing to a test case)
• there are a few files that have skips in them:
  find tests -name test_*.py | xargs fgrep -l pytest.skip
  some of these are because things are unclear, others because
  they need smart split-up in multiple tests with automation
• all test files are kept separate, having only one test. Some should IMHO
  be combined e.g. rendering/test_name_unicode*.py, so the
  output of py.test becomes shorter (but wider with more dots at each filename)
• test coverage is now 53% (but of course stuff is still skipped, it was before changes
  to test_attribute_analyzer was change 74%, why this decreased is unclear to me)
• include tests for test_attribute_analyzer for which result is same for
  combinations of hidden and remove
• include some of the other tests from test_attribute_analyzer

Next step:

• remove skips -> complete coverage