resolve build errors on travis-ci

* travis-ci no longer supports python 2.5

  http://blog.travis-ci.com/2013-11-18-upcoming-build-environment-updates/

  > Python 2.5 has been removed due to very low overall usage and
  > breaking changes in pip and virtualenv.

* GitPython

  pip install no longer supports pre-release versions by default
  http://www.pip-installer.org/en/latest/reference/pip_install.html#pre-release-versions

  resolves build error:

    $ pip install 'GitPython >= 0.2.0' --use-mirrors
    --use-mirrors has been deprecated and will be removed in the future.
    Explicit uses of --index-url and/or --extra-index-url is suggested.
    Downloading/unpacking GitPython>=0.2.0
      Could not find a version that satisfies the requirement
      GitPython>=0.2.0 (from versions: 0.1.7, 0.2.0-beta1, 0.3.0-beta1,
      0.3.0-beta2, 0.3.1-beta2, 0.3.2.RC1)
    Cleaning up...
    No distributions matching the version for GitPython>=0.2.0
provide config for editorconfig plugins

* If a dev adds an editorconfig plugin to their editor,
  automatically configure their editor for code style.

* Specify 4-space softtabs so new code will be compatible
  with Python 3.

* Put the same settings in .gitattributes so git diff
  highlights whitespace errors.
add pep8 tests for syntax errors
add pep8 tests for deprecated python usage
add pep8 tests and fix whitespace errors and warnings
add pep8 tests and fix blank line errors and warnings
add pep8 tests for import errors
add pep8 tests and fix statement errors
add pep8 tests and fix redundant backslashes between brackets
add pep8 tests and fix lexical indentation for python3

These are the pep8 tests that break python3,
such as mixing tabs and spaces for indentation.

I ignored all the pep8 tests that seemed only stylistic,
such as "visual" indentation.

http://docs.python.org/3.3/reference/lexical_analysis.html
add unit tests and fix exception clause compatibility

Exceptions are now compatible with both python 2.5 and 3.3,
and we have unit tests to detect regressions.

The syntax for capturing exceptions changed in python 3, but
we need to continue supporting python 2.5 syntax since many
people use tito on RHEL 5, which has python 2.5.

http://docs.python.org/dev/howto/pyporting.html#capturing-the-currently-raised-exception
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
use explicit relative imports for compatibility

Explicit relative imports work on both python2 and python3.
Resolves error when running `python3 ./runtests.py test/function':

    ERROR: Failure: ImportError (No module named 'fixture')