[Bleeding] Check visibility API for sounds. Fixes BUKKIT-2210

This implementation of a visibility API check for sounds
was created by adding extra methods carrying the source entity
in WorldManager and ServerConfigurationManagerAbstract and
adding a test for canSee in the SCMA sendPacketNearby method.
This approach involves no logic copying, just method addition.
I opted to cast to WorldManager as:
1) IWorldAccess is not in CraftBukkit at the moment
2) There is no other IWorldAccess implemented in CraftBukkit,
  nor is there likely to be one soon. If that day comes, easy fix.

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

@@ -22,6 +22,12 @@ public class WorldManager implements IWorldAccess {
         this.world.getTracker().untrackEntity(entity);
     }
 
+    // CraftBukkit start - Add source entity for a sound.
+    public void a(String s, double d0, double d1, double d2, float f, float f1, Entity sourceentity) {
+        this.server.getServerConfigurationManager().sendPacketNearby(d0, d1, d2, f > 1.0F ? (double) (16.0F * f) : 16.0D, this.world.dimension, new Packet62NamedSoundEffect(s, d0, d1, d2, f, f1), sourceentity);
+    }
+    // CraftBukkit end
+
     public void a(String s, double d0, double d1, double d2, float f, float f1) {
         // CraftBukkit - this.world.dimension
         this.server.getServerConfigurationManager().sendPacketNearby(d0, d1, d2, f > 1.0F ? (double) (16.0F * f) : 16.0D, this.world.dimension, new Packet62NamedSoundEffect(s, d0, d1, d2, f, f1));