0.9.18.2: Win32 exceptions

0.9.18.2: Win32 exceptions
 * Floating point exceptions.
 * Stack exhaustion exception.
 * Rename FIND-INTERRUPTED-NAME to FIND-INTERRUPTED-NAME-AND-FRAME.
 * Commentary (questionary?) on the Win32 exception magic.
 * More groveling.

 Alert: grovel-headers.c/defconstant uses now unsigned long, not long.
 Works on Linux/x86, Win32, and Darwin/ppc. If breaks elsewhere then
 define_signed_const and define_unsigned_const needed.