Add checking for a number of metaclass error conditions.

We add some new rules that are required for preserving internal
invariants of types.

1.  If type (or a subclass of type) appears in bases, it must appear
    before any non-type bases.  If a non-type base (like a regular
    new-style class) occurred first, it could trick type into
    allocating the new class an __dict__ which must be impossible.

2. There are several checks that are made of bases when creating a
   type.  Those checks are now repeated when assigning to __bases__.
   We also add the restriction that assignment to __bases__ may not
   change the metaclass of the type.

Add new tests for these cases and for a few other oddball errors that
were no previously tested.  Remove a crasher test that was fixed.

Also some internal refactoring:  Extract the code to find the most
derived metaclass of a type and its bases.  It is now needed in two
places.  Rewrite the TypeError checks in test_descr to use doctest.
The tests now clearly show what exception they expect to see.

1 files changed, 0 insertions, 19 deletions

diff --git a/Lib/test/crashers/modify_dict_attr.py b/Lib/test/crashers/modify_dict_attr.py
deleted file mode 100644
index dfce467..0000000
--- a/Lib/test/crashers/modify_dict_attr.py
+++ /dev/null
@@ -1,19 +0,0 @@
-
-# http://python.org/sf/1303614
-
-class Y(object):
-    pass
-
-class type_with_modifiable_dict(Y, type):
-    pass
-
-class MyClass(object):
-    """This class has its __dict__ attribute completely exposed:
-    user code can read, reassign and even delete it.
-    """
-    __metaclass__ = type_with_modifiable_dict
-
-
-if __name__ == '__main__':
-    del MyClass.__dict__  # if we set tp_dict to NULL,
-    print MyClass         # doing anything with MyClass segfaults