Cleanup of xboard.c

Cleanup of xboard.c

Remove AskQuestionProc
A bit of cleanup on xboard.c prototypes
Remove dead file-browser code
Delete vestigial jail code
 All the stuff about jailColor was deleted. Only one fishy thing remains:
 xpmJailSquare seems under some conditions used in BlankSquare to draw a
 'neutral' square. it is set to a copy of a light square image. But in the
 current design 'neutral' means blacked out between board and holdings,
 and even with image use, it should not resemble a light square...
Remove registering of CommentPopDown and TagsPopDown
Merge CopyGameSelection into CopyPositionSelection