Hello,

The attached patch adds a mechanism for unwinding the frame ID.  A frame 
ID uniquely identifies a frame.  It also, unlike the frame chain, has 
room to expand so that it can accomodate more than one stack pointer.

For the moment the patch sets up the frame_id_unwind() code but doesn't 
use it.  That will come shortly when I go to commit the code that 
unwinds the PC before anything else.

I'll look to commit in a few days,
Andrew