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/Include/code.h b/Include/code.h
index e9b7906..334ebab 100644
--- a/Include/code.h
+++ b/Include/code.h
@@ -24,6 +24,7 @@
     PyObject *co_name;		/* string (name, for reference) */
     int co_firstlineno;		/* first source line number */
     PyObject *co_lnotab;	/* string (encoding addr<->lineno mapping) */
+    void *co_zombieframe;     /* for optimization only (see frameobject.c) */
 } PyCodeObject;
 
 /* Masks for co_flags above */