[!] Possibly broken imlib2 / libgif detected - ignoring test results

Imlib2 1.4.7 with giflib 5.1.2 is unable to load GIF images.  On x86 / x86_64
this applies to most gifs which are not the first file in the filelist, while
on mips/mipsel and (some?) arm boxes it is unable to load any gif files. Since
feh's tests include gifs, they fail.

As there's nothing we can do about it (and other image formats still work
fine), we'll just pretend everything's okay.

See <https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=813729> for details.
