Since commit d916fedf, GIMP has had the hidden feature to salvage
images (if possible) during a crash into a backup folder. This commit
finishes the feature by opening a dialog proposing to try and recover
the salvaged images.
This is not perfect yet since it doesn't "remember" the XCF path (in
case it was a previously saved image). The images open as new unsaved
and dirty images, but directly from the contents at crash time. For now,
it is up to people to figure out what they correspond to, if relevant.