vagrant 1.1 style plugin loading
vagrant 1.1 style plugin loading

inspired by AWS plugin, raise an error, when not running in a vagrant environment
no longer use ruby 1.8 backwards compatibility Strings, since vagrant 1.1 depends on ruby 1.9

dotless-de/vagrant-vbguest,dotless-de/vagrant-vbguest,roidelapluie/vagrant-vbguest,wizonesolutions/vagrant-parallels-tools,LalatenduMohanty/vagrant-vbguest,nishaya/vagrant-vbguest,giabao/vagrant-vbguest