[Catalog-sig] PyPI XML-RPC multicall support

["Martin v. Löwis"]

The PyPI XML-RPC server now supports multicalls, with a limit
of 100 subcalls per multicall. So if you have an XML-RPC
application that makes thousands of calls to PyPI in a short
time, consider batching them. I was able to obtain a speedup
of four in an application that tries to get all release data
and urls.

Regards,
Martin