Added Python 3.3 support

This fixes many of the old-style relative imports that were left
within the code.  These imports are not valid in Python3, and have
been replaced by absolute imports as well as new-style relative
imports.  The incorrect imports were replaced by absolute imports,
as they are the most consistent and are unlikely to change in the
future.

In a few cases, module were moved and needed to be imported with
an alias to maintain backwards compatibility.  We should consider
moving these imports into a `compat` file, to make it easier to
fix these imports across the entire application.