Warn about changes to CWD on every machine action

Whenever the path where the machine was first created changes, Vagrant
will now show just one warning when an action is run on the machine.

The idea is that if a user copies the machine over to a different
directory with the idea of running two different machines, this warning
will now help the user determine how to make that work.

lib/vagrant/machine.rb

@@ -170,6 +170,8 @@ module Vagrant
       # Extra env keys are the remaining opts
       extra_env = opts.dup
 
+      check_cwd
+
       # Create a deterministic ID for this machine
       vf = nil
       vf = @env.vagrantfile_name[0] if @env.vagrantfile_name
@@ -559,5 +561,25 @@ module Vagrant
       return nil if !@data_dir
       @data_dir.join("creator_uid")
     end
+
+    def check_cwd
+      vagrant_cwd_filepath = @data_dir.join('vagrant_cwd')
+      vagrant_cwd = if File.exist?(vagrant_cwd_filepath)
+        File.read(vagrant_cwd_filepath).chomp
+      end
+
+      if vagrant_cwd
+        if vagrant_cwd != @env.cwd.to_s
+          ui.warn(I18n.t(
+            'vagrant.moved_cwd',
+            old_wd:     vagrant_cwd,
+            current_wd: @env.cwd.to_s))
+
+          File.write(vagrant_cwd_filepath, @env.cwd)
+        end
+      else
+        File.write(vagrant_cwd_filepath, @env.cwd)
+      end
+    end
   end
 end

templates/locales/en.yml

@@ -165,6 +165,10 @@ en:
       description of what they do.
 
       %{list}
+    moved_cwd: |-
+      This machine used to live in %{old_wd} but it's now at %{current_wd}.
+      Please change the name of the machine if you want to run it as a different
+      machine.
     guest_deb_installing_smb: |-
       Installing SMB "mount.cifs"...
     global_status_footer: |-