[rfa] i386-tdep.c: add some insn's to prologue analyzer

[Michael Elizabeth Chastain]

All right!  Thanks!

> I think we should consider the "xor" and "sub" instructions only part of
> the prologue if they're followed by the "mov %esp, %ebp".

Sounds okay to me.  But I was looking at Jim Blandy's generic "abstract
interpreter" code in s390-tdep.c.  I think this would be a good
framework for every prologue interpeter.  Right now, it is simple
longest-match, but it could be enhanced to do this too.

> Can you check whether it really solves the problems you were seeing.

Yes.  I can report back in a couple of hours, and I will have the
next full regression report tomorrow.

Michael C