SPIGOT-738: Return explosion source for Fireball-induced explosions

nms-patches/Explosion.patch

@@ -144,3 +144,15 @@
                  }
              }
          }
+@@ -197,7 +266,10 @@
+     }
+ 
+     public EntityLiving c() {
+-        return this.source == null ? null : (this.source instanceof EntityTNTPrimed ? ((EntityTNTPrimed) this.source).getSource() : (this.source instanceof EntityLiving ? (EntityLiving) this.source : null));
++        // CraftBukkit start - obtain Fireball shooter for explosion tracking
++        // PAIL: Rename
++        return this.source == null ? null : (this.source instanceof EntityTNTPrimed ? ((EntityTNTPrimed) this.source).getSource() : (this.source instanceof EntityLiving ? (EntityLiving) this.source : (this.source instanceof EntityFireball ? ((EntityFireball) this.source).shooter : null)));
++        // CraftBukkit end
+     }
+ 
+     public void clearBlocks() {