These are all added by GDK. We query GDK to see what formats it can
import and then use all of those. So, if a particular version of GDK
isn't compiled with a format it won't so up. Plus, we should be able to
import other formats with GDK loaders if they are available (I think
someone is working on a RAW loader).
With the above hint I got a list of file types supported by GDK using a
Perl script I modified from the web: