raise an error when trying to make a rule with both hash conditions and a block - closes #269

lib/cancan/rule.rb

@@ -11,6 +11,7 @@ module CanCan
     # and subject respectively (such as :read, @project). The third argument is a hash
     # of conditions and the last one is the block passed to the "can" call.
     def initialize(base_behavior, action, subject, conditions, block)
+      raise Error, "You are not able to supply a block with a hash of conditions in #{action} #{subject} ability. Use either one." if conditions.kind_of?(Hash) && !block.nil?
       @match_all = action.nil? && subject.nil?
       @base_behavior = base_behavior
       @actions = [action].flatten