[build] bump libxml2 to 2.7.6 from xmlsoft.org
[build] bump libxml2 to 2.7.6 from xmlsoft.org

Apparently the releases on the GNOME FTP site are really old.

mono/bockbuild,BansheeMediaPlayer/bockbuild,bl8/bockbuild,BansheeMediaPlayer/bockbuild,bl8/bockbuild,bl8/bockbuild,BansheeMediaPlayer/bockbuild,mono/bockbuild