Image path in title bar should update when changed with primImagePath:, not just when saving

[daniels220]

I noticed that using Smalltalk backupImageInFileNamed: 'backup.image' leaves the original running image displaying the backup name in its titlebar, even though Smalltalk imagePath returns the original path. I believe the issue is that the titlebar is updated in the snapshot primitive instead of when the image path is set—so the snapshot that creates the backup updates it, but until we save the image again under its original name, we're stuck with the wrong title bar text.