! When resizing images to JPEG (i.e. thumbnails), allow for variable compression but default to 82 which as per http://www.simplemachines.org/community/index.php?topic=490653.0 is a good balance between quality and size. I *think* I got the right functions for IM/MW but it's hard to tell because the docs are so poor at explaining the difference between the pairs of functions that are appropriate. I'm still not sure a setting is really needed so leave it configurable with a hidden setting and we can give it a UI later if desired.

Signed-off-by: Peter Spicer <sleeping@myperch.org>