Fixed compilation error in change host name capability
Added vagrant 1.1.x backwards compatbility

Since upgrading the plugin API to vagrant 1.2.x it broke compatbility with vagrant 1.1.x. This commit attempts to reify the vagrant 1.1.x compatiblity while not breaking 1.2.x.
Fixed plugin.rb issues with vagrant 1.1

Checks for Vagrant 1.1.x or higher and not 1.2.x or higher. Only monkey patch the vm config object when running under Vagrant 1.2 or higher.