Hello,

The attached tweaks trad-frame so that .addr==-1, instead of .addr==0, 
is used as a reserved value.

A common trick in existing code is to initially set .addr to a cardinal 
offset and then later add that to the inner-most stack address. 
Reserving .addr==0 precluded an edge case.  This adjusts things, at the 
same time adding predicate methods to test for the different possible 
trad-frame saved-reg states.

I'll commit this to the mainline in a few days,
Andrew