Added support for //stack [-a] to not stack air.

src/com/sk89q/worldedit/commands/RegionCommands.java

@@ -205,6 +205,7 @@ public class RegionCommands {
     @Command(
         aliases = {"/stack"},
         usage = "[count] [direction]",
+        flags = "a",
         desc = "Repeat the contents of the selection",
         min = 0,
         max = 2
@@ -219,7 +220,7 @@ public class RegionCommands {
                 args.argsLength() > 1 ? args.getString(1).toLowerCase() : "me");
 
         int affected = editSession.stackCuboidRegion(session.getRegion(),
-                dir, count, true);
+                dir, count, !args.hasFlag('a'));
         player.print(affected + " blocks changed. Undo with //undo");
     }
 }