Travis CI integration

Travis CI (http://travis-ci.org) integrates with Github and allows to run tests in configurable virtual machine for each commit/branch/pull request to Github repository.  It cannot replace http://buildbot.buildbot.net, but adds easy option for developers to run tests on several environments without administrative access to http://buildbot.buildbot.net. 

This merge request contains Travis configuration (in .travis.yml) and patches for Buildbot installation script (setup.py).

In Travis configuration file I reproduced tests configurations similar to http://buildbot.buildbot.net configurations (Python 2.5-2.7, different Twisted, SQLAlchemy and SQLAlchemy-migration versions).

setup.py was patched for easier Buildbot installation on Python 2.5 platform: several Buildbot dependencies doesn't support Python 2.5; pip and easy_install cannot check is package version supported on current platform and always installs latest available version. This is a hack that helps with Buildbot installation, actual bug filled to pip bug tracker: https://github.com/pypa/pip/issues/1115.

To enable Travis for Buildbot github account you should follow simple configuration procedure described  at http://about.travis-ci.org/docs/user/getting-started/.

Results for running Travis in my repository can be found here: https://travis-ci.org/vrutsky/buildbot

This is still Work-In-Progress --- exclude part, that should disable running some tests on Python 2.5 platform doesn't work, but current result already useful.