Re: [Bug-XBoard] [bug #27153] Pre-move does not work on xboard 4.4beta1

[h.g. muller]

indeed, we got it now. It was just tht no one told that the problem was
entering recaptures as pre-moves. In click-click mode this is not possible,
as clicking a new own piece selects it as new from square rtaher than
to square. But I never realized that this ambiguity does not occur for
drag-drop moves, and that 'capture-own' premoves are actualy supposed
to work there. I thought they were to be treated like the click-click moves,
which is why I moved the code there. My mistake.

As the comment shows I misjudged the function of this code. I thought
it was for filtering out illegal premoves, but in fact it is to give precedence
for selection of a new piece in click-click mode over entering an own
capture.

I have already fixed it in WinBoard, and now I am rewriting the XBoard
mouse handler to use the altered back-end as well as to include the
promotion-popup fix. And now that I am at it, I might s well include
the promotion-piece selection of holdings pieces for Superchess and
Great Shatranj.

In fact this seems to lead to so much duplication of code, that I am
considering to move most of the mouse handler to the back-end,
calling it as mouse(UPCLICK); and mouse(DOWNCLICK); from
the respective front-ends.