Issue #12149: Update the method cache after a type's dictionnary gets cleared by the garbage collector. This fixes a segfault when an instance and its type get caught in a reference cycle, and the instance's deallocator calls one of the methods on the type (e.g. when subclassing IOBase). Diagnosis and patch by Davide Rizzo.

--- a/Objects/typeobject.c	Sat Jul 09 21:29:36 2011 +0200
+++ b/Objects/typeobject.c	Tue Jul 12 22:04:20 2011 +0200
@@ -1013,6 +1013,8 @@
     assert(basedealloc);
     basedealloc(self);
 
+    PyType_Modified(type);
+
     /* Can't reference self beyond this point */
     Py_DECREF(type);