Renames some test files to be run in parallel.

All test files named 'paralleltest_.*.py' should be run with

    $ mpiexec -n <np> nosetests -i 'paralleltest_\w+'

or a similar expression for the unittest discovery mechanism.
Simplify travis.yml, move testing stuff to Makefile.
Adds requirements.txt file for pip install in travis.
Fix requirements.txt syntax.
Makes explicit the versions of pip packages.
Updates pyzmq version in travis.yml
Try without explicit version numbers.
See `pip freeze` output.
Remove commented lines in travis.yml
Merge pull request #73 from enthought/bugfix/no-skip

Looks good to me.