rfc: merge create_new_frame() and get_prev_frame()

[Andrew Cagney]

Hello,

(How to clean this up has been bugging me for a long long time).

At present GDB has two functions for creating a frame:

	frame1 = get_prev_frame (frame1);
and
	create_new_frame (read_fp (), read_pc ())

The functions are implement using a convoluted list of architecture 
methods and no one has been clear on how they really do/should work.

I've known that the latter, create_new_frame, was going to need an 
overhaul - instead of read_fp() and read_pc() as parameters it should 
take the entire bank of hardware registers.  Thus create_new_frame() 
would be replaced with:

	new_frame (registers)

(`registers' ~= read_register_gen())

I think I've finally figured out what to do with get_prev_frame().

I think in essence, get_prev_frame() is just a wrapper around 
``new_frame()'' that is:

	get_prev_frame(frame)
	{
	  if (frame->prev == NULL)
	    new_frame (frame->registers)
	  else
	    frame->prev
	}

(frame->registers ~= get_saved_register (frame), it is recursive).

This is because, in all cases, the frame is created using the registers 
and the stop address of the current function.

I'll look to change-request this in a few days.

thoughts?
Andrew