Related to previous commit. Experimenting to get diffcol gs2 checkout on 64 bit linux to work again: this time gnome-lib's devel.bash now adds include/libxml2 to the include paths for CPFLAGS, CPPFLAGS, CXXFLAGS, in order to help yaz find tree.h there. If this works, need to adjust all remaining devel.bash in gnome-lib, gnome-lib-minimal and in src folder.