FIXNUM considered useful

[Daniel L. Weinreb <DLW@QUABBIN.SCRC.Symbolics.COM>]

Scott, I feel that the only point is to recognize explicitly in the spec
and manual that using FIXNUM creates a real hazard that your program may
not be portable.  You, personally, clearly understand what the issue is,
and I'm sure you know that even though within your own environment you
haven't run into problems, nevertheless different programs, or more
exotic implementations, might cause a program to not port correctly.
The only real point here is that everyone who reads the spec should
understand it, too.  As long as it's clear what FIXNUM does mean and
does not mean, then people can make a well-informed choice about whether
to use it or not, and everything should be fine.  But in a language spec
that is devoted to providing program portability, any language feature
that has known non-portable aspects to it should be clearly marked as such.