Blow up if using vagrant < 1.4.0

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 BACKWARDS INCOMPATIBILITY:
 
+  - Support for Vagrant < 1.4 is gone, please use a previous plugin version if
+    you are running Vagrant 1.2 / 1.3
   - Automatic handling of multiple machine scoped cache dirs from versions
     prior to 0.3.0 of this plugin was removed.
   - Support for `enable_nfs` has been deprecated and will be removed on 0.7.0,

lib/vagrant-cachier/plugin.rb

@@ -1,3 +1,9 @@
+# TODO: Switch to Vagrant.require_version before 1.0.0
+#       see: https://github.com/mitchellh/vagrant/blob/bc55081e9ffaa6820113e449a9f76b293a29b27d/lib/vagrant.rb#L202-L228
+unless Gem::Requirement.new('>= 1.4.0').satisfied_by?(Gem::Version.new(Vagrant::VERSION))
+  raise 'vagrant-cachier requires Vagrant >= 1.4.0 in order to work!'
+end
+
 require_relative 'provision_ext'
 Vagrant::Action::Builtin::Provision.class_eval do
   include VagrantPlugins::Cachier::ProvisionExt