This is an extension containing a few demo plug-ins. This is good to
demonstrate the extension format. It will also allow to disable these
plug-ins (if at some point, one doesn't want to show these demo
plug-ins anymore).

And finally it deals with the fact that our plug-in code is stupid, as
it just tries to find the first executable with the same name (minus
extension) as the plug-in folder. This doesn't go well on Windows, where
the permission system is non-existent. So our code just ends up trying
to run the first file with a similar name in a plug-in folder. As the C
goat-exercise contains both an exe and the C source (and the system
probably returns files in alphabetic order), GIMP under Windows tries to
run the C source instead of the executable (this obviously doesn't go
well).
We could try to do more complex logics, like not aborting if the first
file run fails and try the next one in the plug-in folder. Or maybe just
rename the C file...