Only perform the initial bind for each-* bindings once. Unbinding does not resto…

…re the initial node or remove the marker so el.parentNode is going to be null the second time around. [Closes #165]

@@ -370,6 +370,7 @@ Rivets.binders =
     block: true
 
     bind: (el) ->
+      unless @marker?
         attr = ['data', @view.config.prefix, @type].join('-').replace '--', '-'
         @marker = document.createComment " rivets: #{@type} "
         @iterated = []