Relink Debian packages to libgd3 instead of deprecated libgd2

[Ghostbird]

In Debian 9 the packages libgd2-xpm and libgd2-no-xpm are not available, having been replaced with libgd3.
The provided .deb installers for the stable version therefore do not work (the beta version doesn't compile from source, because of more serious issues).

I found out that if you hack the .deb package to require libgd3 instead and symlink libgd.so.3 to libgd.so.2, the game actually runs fine. So a relatively simple relink to libgd3 and repackage of the .deb file would solve this issue.

[Ghostbird]

That's an issue for the binary packages. Source from Github builds fine, though some packages are not required by CMake, yet the compilation will fail if you do not have them. (libbinutils-dev, libalut-dev)

I'm not sure whether this issue is appropriate here, since it's not about the source. Feel free to close.