Simplify make_package_lines().

Leave generate_messages() as comment if no messages are in the package.
This makes it easier to add them later if needed.

PS:
In general one should distinguish between getting the data and building the
result string. A 'template' for the entire CMakeList.txt would be cleaner
than the current approach.
Fix test_catkinize_cmakelists().

Don't check the entire string but only the relevant parts. Also split the test
in two (the two possible cases) to make it easier to locate the problem.
Add .travis.yml
tweak .travis.yml
Merge branch 'fix_unittests' into travis
Only use python 2.7 and 3.2
This should make it run with python3.
Try python 3.3
Add travis build status icon to README.
Unittest run (but fail) with py3.
Merge branch 'travis' into fix_unittests

Conflicts:
	test/test_with_fixtures.py
rm test_with_fixtures.py and related files.
rm fragile unittest in test_main.py.
autopep8: test_main.py
autopep8: test_catkinize_cmakelists.py
Move is_valid_version to catkinize/utils.py
Move doctest of version_validator to test_utils.py
Execute all unittests.
Merge pull request #29 from sotte/fix_unittests

Fix unittests and add travis support.