Fixes for source code build

This fixes a number of issues with the source code build for Alien::LibXML.

 1. Changes the pattern so that the latest version 2.9.1 is preferred over the older 2.9.0
 2. Works around what may be a bug in libxml2's uninstalled .pc file by adding the .libs directory to the library search path (if it is found), note that this fixes rt#90273 reported last November.
 3. Disables python in build, installing with the python enabled tried to install python libraries into system directories which usually fails for normal users.

I am one of the core `Alien::Base` developers, and am keen to see this library be more reliable.  If you don't have the time or interest in this dist, I'd be happy to take over for you.