netpbm: Update to 10.66.00

Also, borrow a tarball from Gentoo so we don't have to use
fetchsvn. And don't depend on libX11 by default.
test-driver: Use netpbm instead of imagemagick

Imagemagick pulls in 100s of megabytes of dependencies.
Installer test: Use the minimal ISO

So we don't depend on KDE etc. (which we don't even test here).