Add Vagrantfile used to diagnose Travis issues

Now that the issue has been resolved, I don't need the Vagrant box any
more. But there might be new issues in the future, and so it might be
useful to keep this file around.

Vagrantfile

@@ -0,0 +1,17 @@
+# This Vagrant box is similar to the environment Travis CI provides. It can be
+# helpful to diagnose Ubuntu-specific issues. (Fontconfig can be ... difficult.)
+
+Vagrant.configure("2") do |config|
+  config.vm.box = "ubuntu/precise64"
+
+  config.vm.provider "virtualbox" do |vb|
+    vb.memory = "1024"
+  end
+
+  config.vm.provision "shell", inline: <<-SHELL
+    apt-get update
+    apt-get install -y git fonts-cantarell libcairo2-dev
+    curl -sL https://static.rust-lang.org/rustup.sh -o /tmp/rustup.sh
+    chmod a+rx /tmp/rustup.sh
+  SHELL
+end