Remove duplicates from "/simple" index page

After uploading both an egg file and a source file for packages with a
hyphen in the name, the "/simple" index lists two entries-- one with
hyphens and one with underscores. For example, if an egg and tarball for
MySQL-python are uploaded, the "/simple" index page lists
"MySQL-python"" and "MySQL_python"".

Some example packages that exhibit this behavior:

- MySQL-python
- Flask-Actions
- unittest-xml-reporting
- nose-exclude

Note that http://pypi.python.org/simple does not list both names with
hyphens and names with underscores, so this change brings pypiserver
closer to the behavior of http://pypi.python.org/simple.

We use the pypiserver project at our company and are interested in
seeing this fixed. I noticed the first fix I submitted didn't properly
handle packages with underscores in their names, so I have re-worked the
fix to handle this.

Thanks,
Eliot