Maintain a valid state in event of IOError 

Installation died on me because LONG_DESCRIPTION wasn't defined. It was defined only in the `try` portion of `setup.py`, with `except IOError` doing nothing (`pass`). So then later of course `long_description=LONG_DESCRIPTION` threw an error.

To make it work, I just aliased `LONG_DESCRIPTION` to `DESCRIPTION` when the `IOError` is raised. Also printed a warning. Which doesn't feel like good form, but importing logging felt like overkill. Maybe doing nothing is the way to go?