Adds backwards compatibility comment

lib/fog/openstack/models/volume/volumes.rb

@@ -8,7 +8,9 @@ module Fog
       class Volumes < Fog::Collection
         model Fog::Volume::OpenStack::Volume
 
-        def all(options = true)
+        def all(options = {:detailed => true})
+          # the parameter has been "detailed = true" before. Make sure we are
+          # backwards compatible
           detailed = options.is_a?(Hash) ? options.delete(:detailed) : options
           load(service.list_volumes(detailed, options).body['volumes'])
         end