This is Neil's fix for SF bug 535905 (Evil Trashcan and GC interaction).
The fix makes it possible to call PyObject_GC_UnTrack() more than once
on the same object, and then move the PyObject_GC_UnTrack() call to
*before* the trashcan code is invoked.
BUGFIX CANDIDATE!
diff --git a/Objects/frameobject.c b/Objects/frameobject.c
index cf3d73a..8e4c60f 100644
--- a/Objects/frameobject.c
+++ b/Objects/frameobject.c
@@ -67,8 +67,8 @@
PyObject **fastlocals;
PyObject **p;
+ PyObject_GC_UnTrack(f);
Py_TRASHCAN_SAFE_BEGIN(f)
- _PyObject_GC_UNTRACK(f);
/* Kill all local variables */
slots = f->f_nlocals + f->f_ncells + f->f_nfreevars;
fastlocals = f->f_localsplus;