fix adding collection helpers to bins

lib/fog/bin.rb

@@ -42,14 +42,16 @@ module Fog
         if availability
           for service in services
             for collection in self[service].collections
+              unless self.respond_to?(collection)
                 self.class_eval <<-EOS, __FILE__, __LINE__
-                def #{collection}
+                  def self.#{collection}
                     self[:#{service}].#{collection}
                   end
                 EOS
               end
             end
           end
+        end
 
         availability
       end