[PATCH] i386: Do backtrace fallback too

Similar patch to earlier x86-64 patch. When the dwarf2 unwinder fails
dump the left over stack with the old unwinder.

Also some clarifications in the headers.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>