Sounds stupid but according to
http://wixtoolset.org/documentation/manual/v3/xsd/http/
there is an extension as part of the WIX toolset that allows things like reserving URL's (which is something I have to do).
I sadly do not find any reference in which URL this is installed.
I am already adding WixNetFxExtension and WixUtilExtension but I fail to find a WixHttpExtension.dll. I have installed the current version, and the documentation contains this schema. So, which assembly (and where is it) do I have to add?
WixHttpExtension is new to WiX v3.10 and v4.0. The first build of WiX v3.10 is available; see http://www.joyofsetup.com/2014/11/25/wix-v3-10-begins-and-is-already-mostly-done/ for details.