Give a useful error if the VirtualBox.xml is not found [close GH-30]

lib/vagrant/env.rb

@@ -51,6 +51,23 @@ msg
 Vagrant has detected that you have VirtualBox version #{version} installed!
 Vagrant requires that you use at least VirtualBox version 3.1. Please install
 a more recent version of VirtualBox to continue.
+msg
+        end
+
+        if !VirtualBox::Global.vboxconfig?
+          error_and_exit(<<-msg)
+Vagrant couldn't find your global VirtualBox.xml file!
+
+If you just recently installed VirtualBox, make sure you've launched
+it at least once, since the initial launch will typically create this
+file.
+
+Otherwise, you may need to set the path to the VirtualBox.xml file
+manually. Note that 90% of people should never have to do this, so
+don't be afraid to use the various Vagrant support lines to ask for
+help. To set the path manually:
+
+VirtualBox::Global.vboxconfig = "/path/to/VirtualBox.xml"
 msg
         end
       end

test/vagrant/env_test.rb

@@ -17,7 +17,15 @@ class EnvTest < Test::Unit::TestCase
 
   context "checking virtualbox version" do
     setup do
-      VirtualBox::Command.stubs(:version)
+      VirtualBox::Command.stubs(:version).returns("3.1.4")
+      VirtualBox::Global.stubs(:vboxconfig?).returns(true)
+    end
+
+    should "not error and exit if everything is good" do
+      VirtualBox::Command.expects(:version).returns("3.1.4")
+      VirtualBox::Global.expects(:vboxconfig?).returns(true)
+      Vagrant::Env.expects(:error_and_exit).never
+      Vagrant::Env.check_virtualbox!
     end
 
     should "error and exit if VirtualBox is not installed or detected" do
@@ -31,6 +39,12 @@ class EnvTest < Test::Unit::TestCase
       VirtualBox::Command.expects(:version).returns("3.0.12r1041")
       Vagrant::Env.check_virtualbox!
     end
+
+    should "error and exit if the the vboxconfig is not set" do
+      VirtualBox::Global.expects(:vboxconfig?).returns(false)
+      Vagrant::Env.expects(:error_and_exit).once
+      Vagrant::Env.check_virtualbox!
+    end
   end
 
   context "requiring a VM" do