Make freeimage backend have preceedence over libjpeg
Make freeimage backend have preceedence over libjpeg

The current implementation of freeimage backend automatically rotates the
images based on EXIF info. Libjpeg backed doesn't do that (although libjpeg
itself may be able to, I didn't check). This commit makes Imv use freeimage for
jpeg files when both backends are available to enable automatic image rotation
when possible.

A cleaner solution could be to add automatic rotaiton functionality to libjpeg
backend as well, but this quick hack is better than nothing ☺

eXeC64/imv,eXeC64/imv