__qualname__ and nested class naming fixes (#1171)

A few fixes related to how we set `__qualname__` and how we show the
type name in function signatures:

- `__qualname__` isn't supposed to have the module name at the
beginning, but we've been putting it there.  This removes it, while
keeping the `Nested.Class` name chaining.

- print `__module__.__qualname__` rather than `type->tp_name`; the
latter doesn't work properly for nested classes, so we would get
`module.B` rather than `module.A.B` for a class `B` with parent `A`.
This also unifies the Python 3 and PyPy code.  Fixes #1166.

- This now sets a `__qualname__` attribute on the type (as would happen
in Python 3.3+) for Python <3.3, including PyPy.  While not particularly
important to have in earlier Python versions, it's useful for us to be
able to extracted the nested name, which is why `__qualname__` was
invented in the first place.

- Added tests for the above.

tests/test_class.py

@@ -44,6 +44,31 @@ def test_docstrings(doc):
     """
 
 
+def test_qualname(doc):
+    """Tests that a properly qualified name is set in __qualname__ (even in pre-3.3, where we
+    backport the attribute) and that generated docstrings properly use it and the module name"""
+    assert m.NestBase.__qualname__ == "NestBase"
+    assert m.NestBase.Nested.__qualname__ == "NestBase.Nested"
+
+    assert doc(m.NestBase.__init__) == """
+        __init__(self: m.class_.NestBase) -> None
+    """
+    assert doc(m.NestBase.g) == """
+        g(self: m.class_.NestBase, arg0: m.class_.NestBase.Nested) -> None
+    """
+    assert doc(m.NestBase.Nested.__init__) == """
+        __init__(self: m.class_.NestBase.Nested) -> None
+    """
+    assert doc(m.NestBase.Nested.fn) == """
+        fn(self: m.class_.NestBase.Nested, arg0: int, arg1: m.class_.NestBase, arg2: m.class_.NestBase.Nested) -> None
+    """  # noqa: E501 line too long
+    assert doc(m.NestBase.Nested.fa) == """
+        fa(self: m.class_.NestBase.Nested, a: int, b: m.class_.NestBase, c: m.class_.NestBase.Nested) -> None
+    """  # noqa: E501 line too long
+    assert m.NestBase.__module__ == "pybind11_tests.class_"
+    assert m.NestBase.Nested.__module__ == "pybind11_tests.class_"
+
+
 def test_inheritance(msg):
     roger = m.Rabbit('Rabbit')
     assert roger.name() + " is a " + roger.species() == "Rabbit is a parrot"
@@ -229,7 +254,9 @@ def test_reentrant_implicit_conversion_failure(msg):
     # ensure that there is no runaway reentrant implicit conversion (#1035)
     with pytest.raises(TypeError) as excinfo:
         m.BogusImplicitConversion(0)
-    assert msg(excinfo.value) == '''__init__(): incompatible constructor arguments. The following argument types are supported:
-    1. m.class_.BogusImplicitConversion(arg0: m.class_.BogusImplicitConversion)
+    assert msg(excinfo.value) == '''
+        __init__(): incompatible constructor arguments. The following argument types are supported:
+            1. m.class_.BogusImplicitConversion(arg0: m.class_.BogusImplicitConversion)
 
-Invoked with: 0'''
+        Invoked with: 0
+    '''