ImageMagick support does not deactivate the other loaders. They all live
together. Of course there will then be situations when its not clear
which loader should be used, because there are several candidates
available. The ImageMagick loader can be configured so it does not try
to load particular image formats, with imagemagick-types-inhibit. Which
particular loader gets used in a particular case is not completely
obvious however. I've made no attempt to change loader priorities, and
Imagemagick usualy gets last shot at loading a format, so when jpeg
support is compiled in, and imagemagick support is compiled in, the jpeg
loader wins by default.