Previously stomped the shared GServer->MOVE_SPEED_MOD movement-timing
divisor, which character.cpp's UpdatePosition also uses for monster position
interpolation -- GM testing broke movement/attack range server-wide until
restart. Now stores a per-character SpeedModPercent that GetMoveSpeed()
applies on every recompute, so it survives future SetStats() calls instead
of being silently overwritten back to base speed. Also fixes Mspd_base (the
value actually broadcast to clients) never being set while WALKING.
Thomas