BST: allow ALT + mouse button 1 as movement alternative to button 2
BST: allow ALT + mouse button 1 as movement alternative to button 2

tim-janik/beast,tim-janik/beast,GNOME/beast,tim-janik/beast,GNOME/beast,swesterfeld/beast,swesterfeld/beast,swesterfeld/beast,tim-janik/beast,swesterfeld/beast,tim-janik/beast,swesterfeld/beast,swesterfeld/beast,swesterfeld/beast,GNOME/beast,tim-janik/beast,GNOME/beast,tim-janik/beast,GNOME/beast,GNOME/beast,GNOME/beast