Fix for eat_apple jitter; increase length at head end

In previous logic the new segment was appended at tail end according to
current direction.
1) This caused a 1-fps-cycle jitter (reason undetermined)
2) For a turning snake, the direction of tail segments needs not be the
current direction of head segment.

In the fix the new segment is appended at the head, according to current direction.
So the move_X functions need not be called here again.