remove any lingering raw_inputs on raw_input

There should never be more than one,
so ensure that is the case on creation.

closes  #3710

IPython/html/static/notebook/js/outputarea.js

@@ -545,7 +545,10 b' var IPython = (function (IPython) {'
         this.expand();
         this.flush_clear_timeout();
         var area = this.create_output_area();
-
+        
+        // disable any other raw_inputs, if they are left around
+        $("div.output_subarea.raw_input").remove();
+        
         area.append(
             $("<div/>")
             .addClass("box-flex1 output_subarea raw_input")