Vary the behaviour of Mines's solve function depending on whether the

Vary the behaviour of Mines's solve function depending on whether the
user is already in the 'dead' state when they press it. If so, we
reveal the rest of the mines in the grid as if it were the Windows
Minesweeper 'you lose' display, which provides information showing
what the user got wrong. (Otherwise they have to repeatedly flick back
and forth between Solve and Undo if they want to work out which flag
they placed wrongly.)

If you press Solve while alive, however, the existing behaviour
remains unchanged.

(This feature was suggested by Clive Jones a couple of weeks after I
first wrote Mines, and I've finally got round to doing it!)

[originally from svn r9561]