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.
Merge pull request #2 from eternalthinker/jitterfix

Fix for eat_apple jitter; increase length at head end