implement __nonzero__ for HTMLProperty

Author: Richard Jones

roundup/cgi/templating.py

@@ -1018,6 +1018,9 @@ def __cmp__(self, other):
             return cmp(self._value, other._value)
         return cmp(self._value, other)
 
+    def __nonzero__(self):
+        return not not self._value
+
     def isset(self):
         '''Is my _value not None?'''
         return self._value is not None