last commit did not include nbconvert.py change to not reread the file -- adding now

nbconvert.py

@@ -182,6 +182,7 b' class Converter(object):'
 
     def render(self):
         "read, convert, and save self.infile"
+        if not hasattr(self, 'nb'):
         self.read()
         self.output = self.convert()
         return self.save()