This patch improves and simplifies the criteria for whether or not to draw a frame and a shadow around an image's thumbnail. The old size-based detection code was unreliable and gave false positives as well as false negatives. It is replaced with a simple check for whether the image has an alpha channel, which not only automatically matches all icon files, but also non-icon raster images with transparency, which look better without the frame.
BUG: 258514
FIXED-IN: 5.50