Update from upstream SpigotMC

Upstream merge (we must go deeper) SpigotMC/Spigot@1e7bc383c3

CraftBukkit-Patches/0066-Prevent-Mineshaft-Saving.patch

@@ -0,0 +1,20 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: md_5 <git@md-5.net>
+Date: Fri, 13 Dec 2013 15:21:02 +1100
+Subject: [PATCH] Prevent Mineshaft Saving
+
+
+diff --git a/src/main/java/net/minecraft/server/StructureGenerator.java b/src/main/java/net/minecraft/server/StructureGenerator.java
+index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
+--- a/src/main/java/net/minecraft/server/StructureGenerator.java
++++ b/src/main/java/net/minecraft/server/StructureGenerator.java
+@@ -0,0 +0,0 @@ public abstract class StructureGenerator extends WorldGenBase {
+     private void a(World world) {
+         if (this.e == null) {
+             // Spigot Start
+-            if ( world.spigotConfig.saveStructureInfo )
++            if ( world.spigotConfig.saveStructureInfo && !this.a().equals( "Mineshaft" ) )
+             {
+             this.e = (PersistentStructure) world.a(PersistentStructure.class, this.a());
+             } else
+--