Attached is a patch to limit address range in ra-pointer-valid-p() in
debug-int.lisp to make backtrace more accurate.
With this patch, address is valid between #x08048000 to #xBFC00000,
rather than #x00001000 to #xFFFFFFFF on FreeBSD/i386 GENERIC kernel, and
(THROW NO-SUCH-TAG) test does not fail on FreeBSD 5 and later.
I think setting correct value to user_space_start/end will fix tests of
debug.impure.lisp on other systems.
(On Linux/i386, start:end seems to be around #x08000000:#xC0000000, but
I couldn't figure out how to get the exact value.)