Fix hanging in ipcluster.py when already started or stopped.

Now ipcluster.py start/stop won't hang if the cluster is already started
or stopped.

This also changes the usage. The command line arg passed must actually
call the python function you want. Now we can use the script more generally,
for example, starting an arbitrary number of engines.
    $ python ipcluster.py 'start(n=12)'
Makefile directly calls the python functions.
Merge branch 'travis-hangs' of https://github.com/cowlicks/distarray into cowlicks-travis-hangs
Explicitly import print_function from __future__.
Simplify code that prints and deals with 2/3 differences.
Merge pull request #1 from enthought/cowlicks-travis-hangs

Some additions to your travis-hangs PR
Merge pull request #127 from cowlicks/travis-hangs

Fix hanging in ipcluster.py when already started or stopped.