changed click-click moves

changed click-click moves

I got complaints about the way XBoard 4.4.0 handles click-click moves, in particular changing the selected piece after selecting King (for which I suppressed interference with FRC castling in a rather brutal way). People tell me it is very annoying that clicks sometimes don't work to select a piece. WinBoard uses refined logic in the back-end to handle this, but the XBoard front-end is not interfaced with that yet. (This would require a major rewrite of the mouse handler.)

This temporary patch suppresses this behavior in all variants that do not support Fischer castling, and even there only exhibit it for Rook-after-King selection (which will be interpreted as an attempt to enter a castling move as K x own R).