Continue search on ponder hit

Continue search on ponder hit

The usermove command is now examined during ponder search, commparing
the move with the hint move (stored in a new static variable for the
purpose). If there is a ponder hit, the ponder search, which was started
in BACKGROUND_MODE, is switched to FOREGROUND_MODE, and a ResponseTime
is calculated, so that it will pay attention to the clock, and play
a move once it times out. This is recognized by setting the hint-move
text to "hit", which then suppresses retraction of the hint move.
 The if-statement at the top of InputMove is now turned into a 'while',
so that a move produced after a ponder hit will immediately be followed
by pondering over the next move. A ponder miss (or non-move command)
will terminate this loop, through backlogging the command (as will
a failure to produce a hint move).
 The way the thinking time is calculated after a ponder hit might
have to be revised. For now SetTimeControl is called after a ponder hit
when the computer has zero moves left.