Update exception error message handling.

As of python 2.6, using Exception.message is deprecated.  This is a
result of PEP 352.  More info:

http://legacy.python.org/dev/peps/pep-0352/
http://stackoverflow.com/questions/1272138/baseexception-message-deprecated-in-python-2-6
Merge pull request #30 from uber/jr-fix-exception-deprecation-warning

Update exception error message handling.