Your make install error is likely incomplete. Is there any terminal output before those lines? They don't actually explain the error itself. I would try installing the app myself, but a brief read of the instructions makes me nervous about security implications. Also, the installation instructions
here link to
this script intended for use on an Ubuntu system. It is a nice guide on why things could be broken (though running it would not work, obviously). First of all, it seems to rely on gnome (or at least gconf, libgnome-menu and libgnomeui). I'm not sure if it would work without gnome or not -- the configure script appears to be very poorly written (it may just be automatically generated). mplayer seems to be a dependency as well. It looks like flam3 is a dependency, but even without that installed the configure script doesn't complain a bit (though it appears to create a flam3.pc file -- so I think flam3 is probably required even though the terrible configure script isn't complaining). On closer inspection I think the latest stable version tarball (electricsheep-2.6.8.tar.gz) may bundle flam3 with it, so this may not be a concern at all. The README suggests it needs xloadimage, which I don't *think* is present in Slackware.
This seems like a sort of messy project; the stable tarball includes flam3 and mpeg2dec, and I'm not sure if they would overwrite what is already on my system (I have mpeg2dec already). The svn version seems to bundle ffmpeg. The worst part about this is, I don't see a way of disabling ffmpeg, and it doesn't check if ffmpeg is already installed; it just installs it anyway. This is really NOT how a well-written Linux application should work; it should not just bundle and reinstall dependencies (that's the Windows way of doing things). I tried to make a SlackBuild for you, but I don't think I can continue on this without actually installing it to my system (which I refuse to do), and even if I did it would be messy.
Although I don't like the idea of the program, it's the implementation that is really terrible. I would try the svn version I guess and roughly follow the instructions in the linked shell script I guess -- but I would say good luck.