Fix the "Ghost minecart" issue.

This reverts commit 73647864179cbab9f340044e9d33add445fbe774 - "Ignore entity movement packets if distance == 0"

This a commit introduced an intermittent bug which has caused minecart ghosting - they are invisible until you interact with them physically. This is described in leaky bugs:
http://leaky.bukkit.org/issues/547
http://leaky.bukkit.org/issues/563

And caused by the fact that normally when loading a chunk, entities fall with gravity before the block data has been loaded, and are sent a zero-distance packet to reset their positions. See Issue #190:
https://github.com/Bukkit/CraftBukkit/issues/#issue/190

src/main/java/net/minecraft/server/EntityTrackerEntry.java

@@ -71,11 +71,6 @@ public class EntityTrackerEntry {
             boolean flag = Math.abs(i) >= 8 || Math.abs(j) >= 8 || Math.abs(k) >= 8;
             boolean flag1 = Math.abs(l - this.g) >= 8 || Math.abs(i1 - this.h) >= 8;
 
-            // CraftBukkit - Create relative movement packet only if distance is greater than zero.
-            int distanceSquared = j1*j1+k1*k1+l1*l1; 
-            flag = (distanceSquared > 0) && flag;
-            // CraftBukkit stop
-
             if (j1 >= -128 && j1 < 128 && k1 >= -128 && k1 < 128 && l1 >= -128 && l1 < 128) {
                 if (flag && flag1) {
                     object = new Packet33RelEntityMoveLook(this.a.id, (byte) j1, (byte) k1, (byte) l1, (byte) l, (byte) i1);