Hello,

This is the big one.  This patch splits the existing get_prev_frame() in 
two: legacy_get_prev_frame(), and a rewritten get_prev_frame().  Old 
architectures that use the initialization methods:

	INIT_FRAME_EXTRA_INFO
	FRAME_CHAIN
	INIT_FRAME_PC
	INIT_FRAME_PC_FIRST
	FRAME_SAVED_PC

continue to use the old frame initialization sequence (implemented by 
legacy_get_prev_frame()), however new ISAs can instead just implement 
the methods:

	unwind the pc
	unwind the frame's ID
	unwind a register

The d10v, on the cagney-unwind-20030108-branch demonstrates this working.

As part of this change, I moved the `set backtrace-below-main' 
command/code to "frame.c" (from "blockframe.c").  Since the logic was 
moved to get_prev_frame() it can be enabled/disabled without needing to 
flush the frame cache.  Didn't see any regressions with this move.

Following on from this will be patches to add:

- sentinel frame (to simplify the way frames are implemented)

- tradational frame (to simplify the process of updating existing 
architectures)

- reimplement d10v's frame code, so that it uses the new mechanisms

I'm looking to commit this specific change in a few days - need to run 
more tests first ...

comments,
Andrew