Fix namedtuple support

There were a couple issues:
 - namedtuple with one member didn't work
 - namedtuple content access was never possible
 - operator.itemgetter didn't work properly. Corrected py__bool__ for FakeSequence

Fixes #730.

jedi/evaluate/iterable.py

@@ -511,6 +511,9 @@ class FakeSequence(_FakeArray):
     def py__iter__(self):
         return self._lazy_context_list
 
+    def py__bool__(self):
+        return bool(len(self._lazy_context_list))
+
     def __repr__(self):
         return "<%s of %s>" % (type(self).__name__, self._lazy_context_list)