[RFA/powerpc] Add handling for stack-check sequences in prologue

[Joel Brobecker]

> 2008-09-01  Jerome Guitton  <guitton@adacore.com>
> 
> 	* rs6000-tdep.c (rs6000_fetch_instruction)
> 	(rs6000_skip_stack_check): New functions.
> 	(skip_prologue): Skip stack check sequence.

I just reviewed the patch, and it looks OK to me. I think there are
other maintainers who are also interested in powerpc, so give it a
few more days (say until Fri) to see if they might want to comment
and then commit if no objection.

-- 
Joel