Add a "mine" block-art splash screen. This one's not bad.

Add a few (badly drawn) "boom" splash screens, displayed when a mine is
detonated.  I really would like an ANSI/block artist to replace or add to
these with some decent art (Grymmjack, Kirkman?).
Fixed a couple of cosmetic issues I noticed when watching the Minesweeper
YouTube video back, e.g. extra digit on the count-down timer.
Fixed a bug in place_mines() that could place one too-few mines on the board
if the player were extra lucky (the initially selected cell was chosen for a
random mine placement).
When detonating a mine while cloning, display the detonated mine in the file
board screen as detonated (and not a regular/undetonated) mine.