Also include a ‘fresh’ VM for staticness testing

This fresh VM deliberately contains no dependencies and installs nothing, so it can be used to check that the uploaded binary still runs.

Vagrantfile

@@ -1,21 +1,29 @@
 require 'date'
 
 Vagrant.configure(2) do |config|
+
+  # We use Ubuntu instead of Debian because the image comes with two-way
+  # shared folder support by default.
+  UBUNTU = 'ubuntu/xenial64'
+
+  # The main VM is the one used for development and testing.
+  config.vm.define(:exa, primary: true) do |config|
     config.vm.provider :virtualbox do |v|
       v.name = 'exa'
       v.memory = 1024
       v.cpus = 1
     end
 
-    developer = 'ubuntu'
-
-
-    # We use Ubuntu instead of Debian because the image comes with two-way
-    # shared folder support by default.
-    config.vm.box = 'ubuntu/xenial64'
+    config.vm.box = UBUNTU
     config.vm.hostname = 'exa'
 
 
+    # Make sure we know the VM image’s default user name. The ‘cassowary’ user
+    # (specified later) is used for most of the test *output*, but we still
+    # need to know where the ‘target’ and ‘.cargo’ directories go.
+    developer = 'ubuntu'
+
+
     # Install the dependencies needed for exa to build, as quietly as
     # apt can do.
     config.vm.provision :shell, privileged: true, inline: <<-EOF
@@ -419,7 +427,6 @@ Vagrant.configure(2) do |config|
         sudo chmod $perms          "#{test_dir}/permissions/$perms"
         sudo touch -t #{some_date} "#{test_dir}/permissions/$perms"
       done
-
     EOF
 
     old = '200303030000.00'
@@ -614,4 +621,23 @@ Vagrant.configure(2) do |config|
         cargo kcov --print-install-kcov-sh | sudo sh
       EOF
     end
+  end
+
+
+  # Remember that problem that exa had where the binary wasn’t actually
+  # self-contained? Or the problem where the Linux binary was actually the
+  # macOS binary in disguise?
+  #
+  # This is a “fresh” VM that intentionally downloads no dependencies and
+  # installs nothing so that we can check that exa still runs!
+  config.vm.define(:fresh) do |config|
+    config.vm.box = UBUNTU
+    config.vm.hostname = 'fresh'
+
+    config.vm.provider :virtualbox do |v|
+      v.name = 'exa-fresh'
+      v.memory = 384
+      v.cpus = 1
+    end
+  end
 end