[Catalog-sig] ZPT template caching

["Martin v. Löwis"]

I just added template caching to PyPI: rather than parsing
a page template on each request, it caches the templates, and
later renders a pre-parsed one. According to my measurements,
this should reduce the number of Python function calls needed
to render a page noticably.

As a side effect, Apache needs to be restarted when a template
changes (this was already the case for code changes).

Regards,
Martin