Re: Crashes in "C-h h"

[Pip Cet]

> the recent XFIXNUM change.

"The recent XFIXNUM change" I rather cryptically alluded to is that
you're no longer allowed to call XFIXNUM on a Lisp_Object that isn't
FIXNUMP; previously, this was valid in some circumstances, either
because XFIXNUM (non_fixnum_object) wasn't actually ever used (FIXNUMP
check after the XFIXNUM), or because the only thing that was relied on
was that XFIXNUM (Qnil) == 0.

There are two fixes:
- check FIXNUMP
- use XFIXNUM_RAW

The second fix is only available to us if we're definitely sure that
XFIXNUM_RAW will not be used (except, maybe, if we want to introduce a
Qnil-is-0 dependency, in the case of a nil repertory). I don't think
that's the case here.