Fix time forfeits at classical TC

Fix time forfeits at classical TC

GNU Shogi often forfeited in the last move of a classical-TC session,
because its ResponseTime + Extra time could go up to 3.5/3 times
the remaining clock time T: ReponseTime = T/3 and ExtraTime =
10*TCleft = 10*(ResponseTime/4) = 2.5*ResponseTime. To prevent the
number of times ResponseTime can be extended with TCleft (as controlled
by TCcount) is reduced from 10 to 6 + MovesLeft.