bpo-43682: @staticmethod inherits attributes (GH-25268)

Static methods (@staticmethod) and class methods (@classmethod) now
inherit the method attributes (__module__, __name__, __qualname__,
__doc__, __annotations__) and have a new __wrapped__ attribute.

Changes:

* Add a repr() method to staticmethod and classmethod types.
* Add tests on the @classmethod decorator.
diff --git a/Lib/test/test_descr.py b/Lib/test/test_descr.py
index 8c75ec3..79d6c4b 100644
--- a/Lib/test/test_descr.py
+++ b/Lib/test/test_descr.py
@@ -1545,7 +1545,9 @@ class D(C):
         self.assertEqual(d.foo(1), (d, 1))
         self.assertEqual(D.foo(d, 1), (d, 1))
         # Test for a specific crash (SF bug 528132)
-        def f(cls, arg): return (cls, arg)
+        def f(cls, arg):
+            "f docstring"
+            return (cls, arg)
         ff = classmethod(f)
         self.assertEqual(ff.__get__(0, int)(42), (int, 42))
         self.assertEqual(ff.__get__(0)(42), (int, 42))
@@ -1571,10 +1573,16 @@ def f(cls, arg): return (cls, arg)
             self.fail("classmethod shouldn't accept keyword args")
 
         cm = classmethod(f)
-        self.assertEqual(cm.__dict__, {})
+        cm_dict = {'__annotations__': {},
+                   '__doc__': "f docstring",
+                   '__module__': __name__,
+                   '__name__': 'f',
+                   '__qualname__': f.__qualname__}
+        self.assertEqual(cm.__dict__, cm_dict)
+
         cm.x = 42
         self.assertEqual(cm.x, 42)
-        self.assertEqual(cm.__dict__, {"x" : 42})
+        self.assertEqual(cm.__dict__, {"x" : 42, **cm_dict})
         del cm.x
         self.assertNotHasAttr(cm, "x")
 
@@ -1654,10 +1662,10 @@ class D(C):
         self.assertEqual(d.foo(1), (d, 1))
         self.assertEqual(D.foo(d, 1), (d, 1))
         sm = staticmethod(None)
-        self.assertEqual(sm.__dict__, {})
+        self.assertEqual(sm.__dict__, {'__doc__': None})
         sm.x = 42
         self.assertEqual(sm.x, 42)
-        self.assertEqual(sm.__dict__, {"x" : 42})
+        self.assertEqual(sm.__dict__, {"x" : 42, '__doc__': None})
         del sm.x
         self.assertNotHasAttr(sm, "x")