Size namedtuple values

This change includes values when sizing a namedtuple. Before this values were
ignored:

  >>> from pympler import asizeof
  >>> import collections
  >>> Point = collections.namedtuple('Point', ('x', 'y'))
  >>>
  >>> print(asizeof.asized(Point(x=11, y=22), detail=1).format())
  Point(x=11, y=22) size=136 flat=72
      __slots__ size=64 flat=64
      __class__ size=0 flat=0

Now values appear like a tuple's do:

  >>> print(asizeof.asized(Point(x=11, y=22), detail=1).format())
  Point(x=11, y=22) size=184 flat=72
      __slots__ size=64 flat=64
      11 size=24 flat=24
      22 size=24 flat=24
      __class__ size=0 flat=0
  >>> print(asizeof.asized((11, 22), detail=1).format())
  (11, 22) size=120 flat=72
      11 size=24 flat=24
      22 size=24 flat=24

Fixes pympler#35

The modified namedtuple test also passes:

  $ python test/runtest.py --verbose=3 test/asizeof

pympler/asizeof.py

@@ -638,9 +638,12 @@ def _cell_refs(obj, named):
 
 
 def _namedtuple_refs(obj, named):
-    '''Return slots but exclude dict
+    '''Return specific referents of obj-as-sequence and slots but exclude dict.
     '''
-    return _refs(obj, named, '__class__', slots='__slots__')
+    for r in _refs(obj, named, '__class__', slots='__slots__'):
+        yield r
+    for r in obj:
+        yield r
 
 
 def _gen_refs(obj, named):

test/asizeof/test_asizeof.py

@@ -307,14 +307,15 @@ def inner():
         self.assertTrue(size_closure >= size_data, (size_closure, size_data))
 
     def test_namedtuple(self):
-        '''Test namedtuple __dict__ property isn't included
+        '''Test values are included but namedtuple __dict__ isn't.
         '''
         from collections import namedtuple
         Point = namedtuple('Point', ['x', 'y'])
         point = Point(x=11, y=22)
         size = asizeof.asized(point, detail=1)
         refs = [ref.name for ref in size.refs]
         self.assertTrue('__dict__' not in refs, refs)
+        self.assertTrue('11' in refs, refs)
 
 
 class FunctionTest(unittest.TestCase):