This patch lets store_struct_address save the struct_addr in a LIFO
queue, 
from which extract_struct_value_address can then pull it out.  The value
of SP is used as a confidence check, to make sure each struct_addr goes
to the right stack frame.  If the struct_addr isn't found on the queue, 
then the target can fall back to extracting it from a register.

I'm pretty sure this works -- I've tested it on mips, arm, d10v and
i386.
Kevin, would you by any chance be in a position to test it on ia64
and/or
rs6000?

I've included patches for all of the targets that use the infamous
"horrid kludge" from rs6000-tdep.c.  Those will of course have to
be approved by individual maintainers, but the shared code could go
in before then.

Andrew, OK for mips?  Tested, of course...

Michael