Register a (name, servlet) for future "get(name)" requests.
The name must be HTTP-safe -- see RFC 1945 for details.
If the same Servlet is registered multiple times, or
multiple threads attempt the simultaneous register
and unregister of a Servlet, then the order of
"Servlet.init()" and "Servlet.destroy()" is not
defined.
See Also:ServletRegistry.unregister(String)