[RC1] Watermark feature does not support GIF images as logo

[Kirby]

Well, don't know if anybody does need that, but as the Unisys patent has expired and GIFs are still widely used you might want to check if GD does support GIF and if so support this too

ImageMagick should have no problem with gif images. I'll look a little more into what would need to be done so that there will be some more support with GD as well.