It turns out that some calls return AEDesc records that are "borrowed",

the AEDesc data shouldn't be disposed when the Python object is.

Added a C call AEDesc_NewBorrowed() to create these objects and a Python
method old=AEDesc.AutoDispose(onoff) to change auto-dispose state.

Include/pymactoolbox.h

@@ -106,6 +106,7 @@ PyObject *PyMac_BuildFSRef(FSRef *);		/* Convert FSRef to PyObject */
 
 /* AE exports */
 extern PyObject *AEDesc_New(AppleEvent *); /* XXXX Why passed by address?? */
+extern PyObject *AEDesc_NewBorrowed(AppleEvent *);
 extern int AEDesc_Convert(PyObject *, AppleEvent *);
 
 /* Cm exports */