Merge from rjones-funccall branch.

Applied patch zombie-frames-2.diff from sf patch 876206 with updates for
Python 2.5 and also modified to retain the free_list to avoid the 67%
slow-down in pybench recursion test. 5% speed up in function call pybench.
diff --git a/Objects/codeobject.c b/Objects/codeobject.c
index 8ae2399..a9bcb01 100644
--- a/Objects/codeobject.c
+++ b/Objects/codeobject.c
@@ -102,6 +102,7 @@
 		co->co_firstlineno = firstlineno;
 		Py_INCREF(lnotab);
 		co->co_lnotab = lnotab;
+                co->co_zombieframe = NULL;
 	}
 	return co;
 }
@@ -265,6 +266,8 @@
 	Py_XDECREF(co->co_filename);
 	Py_XDECREF(co->co_name);
 	Py_XDECREF(co->co_lnotab);
+        if (co->co_zombieframe != NULL)
+                PyObject_GC_Del(co->co_zombieframe);
 	PyObject_DEL(co);
 }