add unit test and module compatibility lib

Add modules compat lib to support both python 2 and 3, and
add unit test to detect regressions.

Tito uses two modules that have changed significantly between
python 2 and 3:

* commands module merged into subprocess module
* ConfigParser module renamed as configparser
add unit test and use print function for python3 compat

Python 3 does not have the print statement, so convert all
print statements to print functions and add an ugly duckling
unit test to detect regressions.
add python 3.3 to travis-ci build matrix
avoid ImportError in test suite on python 3

python3 does not allow relative imports.

test/unit/__init.py__ and test/functional/__init.py__ already exist,
which means we can use absolute import on all versions of python
without resorting to http://legacy.python.org/dev/peps/pep-0328/
python 2.4 (rhel 5) does not support 'with...as' syntax

resolves from a73c90cb...

    Using Python 2.4
    Using nose 0.1
    Running tito tests against: /home/sandbox/src
    EEEE.Warning: spacewalk.releng.* namespace in tito.props is obsolete. Use tito.* instead.
    Warning: spacewalk.releng.* namespace in tito.props is obsolete. Use tito.* instead.
    ..............................F...........
    ======================================================================
    ERROR: Failure: SyntaxError (invalid syntax (fixture.py, line 159))
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "/usr/lib/python2.4/site-packages/nose/loader.py", line 381, in loadTestsFromName
        module = self.importer.importFromPath(
      File "/usr/lib/python2.4/site-packages/nose/importer.py", line 39, in importFromPath
        return self.importFromDir(dir_path, fqname)
      File "/usr/lib/python2.4/site-packages/nose/importer.py", line 86, in importFromDir
        mod = load_module(part_fqname, fh, filename, desc)
      File "/home/sandbox/test/functional/fetch_tests.py", line 27, in ?
        from fixture import TitoGitTestFixture, tito
      File "/home/sandbox/test/functional/fixture.py", line 159
        with open(os.path.join(full_pkg_dir, 'tito.props'), 'w') \
                ^
    SyntaxError: invalid syntax
docs: createrepo is needed for functional tests