Some further improvements to BlockGeneric

- Only have computers implement custom block drop logic: everything
   else only drops in creative mode.
 - Fix redstone inputs not being received correctly. Introduced in
   8b86a954ee, yes I'm a silly billy.
 - Only update the neighbour which changed.

src/main/java/dan200/computercraft/ComputerCraft.java

@@ -235,7 +235,8 @@ public class ComputerCraft
     }
 
     @Deprecated
-    public static class Upgrades {
+    public static class Upgrades
+    {
         public static TurtleModem advancedModem;
     }