Added playmode command 'C' to set a clock. When the clock runs out the

Added playmode command 'C' to set a clock. When the clock runs out the
game is called a draw. When a clock is set and then set again after
the game has begun if the value of the new clock is less than the
elapsed time of the current clock the time is added. Else the new
clock is the new clock value. Setting the clock to 0 will disable a
running clock. The format in the clock input window is
[1-9][hms][ ]...

SIGINT is now ignored completely.

Catch SIGTERM and exit cleanly.