imlib_render_image_on_drawable_at_size() tended to leave nasty
semi-transparent artifacts in 32-bit mode. Apparently, resizing an
image in 32-bit mode affects the alpha channel even if there is no
transparency in the image. With this patch, resizing is done in
24-bit mode (or whatever depth the original image has) before
converting the image to 32-bit and rendering it on the display.
Origin: https://gist.github.com/fmthoma/f76a1b44e00d5ca972bb
cf. https://github.com/hut/ranger/issues/86#issuecomment-166027119
