Readded `vagrant down` but as an error message to assist users in migrating to `vagrant destroy`

lib/vagrant/commands/down.rb

@@ -0,0 +1,16 @@
+module Vagrant
+  class Commands
+    # `vagrant down` is now `vagrant destroy`
+    class Down < Base
+      Base.subcommand "down", self
+
+      def execute(args=[])
+        error_and_exit(:command_deprecation_down)
+      end
+
+      def options_spec(opts)
+        opts.banner = "Usage: vagrant down"
+      end
+    end
+  end
+end

templates/errors.yml

@@ -42,6 +42,9 @@
   vagrant box add name uri
   vagrant box remove name
   vagrant box list
+:command_deprecation_down: |-
+  `vagrant down` is now `vagrant destroy`. Please use that command instead. This
+  warning will be removed in future versions.
 :dotfile_error: |-
   The dotfile which Vagrant uses to store the UUID of the project's
   virtual machine already exists and is not a file! The dotfile is

test/vagrant/commands/down_test.rb

@@ -0,0 +1,17 @@
+require File.join(File.dirname(__FILE__), '..', '..', 'test_helper')
+
+class CommandsDownTest < Test::Unit::TestCase
+  setup do
+    @klass = Vagrant::Commands::Down
+
+    @env = mock_environment
+    @instance = @klass.new(@env)
+  end
+
+  context "executing" do
+    should "just error and exit" do
+      @instance.expects(:error_and_exit).with(:command_deprecation_down)
+      @instance.execute
+    end
+  end
+end