WIXFEAT:4505 - WixHttpExtension for URL reservations

I tried to find all the places to add the new extension and implement everything, but I might have missed something.

I would like to port this back to v3.x.
I couldn't find any official documentation.  [This blog entry](http://blogs.technet.com/b/askperf/archive/2008/02/03/ws2008-windows-service-hardening.aspx) was the most official thing I found.