move existing tests.py into common module
move VCS-specific code into own testing module

Allows easier testing of only a particular VCS type.
move travis test execution to shell script
make test_* scripts executable as main modules
rewrite travis test script to run one at a time
add a tox.ini file
use py.test as a test runner
run git/svn/hg builds in parallel
add tests/ to PYTHONPATH
fix typo
don't run Hg/Git/Svn tests in parallel
Merge branch 'develop' into feature/refactor-tests

Conflicts:
	tests/common.py
Merge pull request #58 from OEP/feature/refactor-tests

Testing framework improvements