Submit/gtk and more

1) probably helpful: "gnome-autogen.sh: make check_m4macros aware of ACLOCAL_PATH"
2) adding dispcalgui
3) mypaint 3 versions. You may or may not like it. Adding it to this pull request because its the use case for 1)

I suggest merging 1) and 2) and evaluating 3) if you're interested only.

These changes were already found in https://github.com/NixOS/nixpkgs/pull/517