use the new .has_plugin method of the Vagrant object, which is available if your installed version of Vagrant is 1.3.2 or higher, to optionally enable the Landrush and Vagrant Cachier plugins, if they are installed
modified README to include a new requirements section
Merge pull request #6 from hardyoyo/DS-1661-enable-landrush

use the new .has_plugin method of the Vagrant object to optionally enable plugins