[Bug: 21.5-b27] describe-function shows build-time file locations

[Stephen J. Turnbull]

Ron Isaacson writes:

 > Why do these libs need to be built into the binary? Is it just a
 > performance thing?

Yes.  It turns loading the minimal Lisp files from a 5 minute exercise
on a 1GHz Mac to a 5 second startup.  Most Lisp environments have some
similar mechanism.

For ordinary use for Unix users, an XEmacs process may live for many
weeks, and it's no big deal.  For many Windows users, rebooting daily
(or more frequently) it's a noticable annoyance.  For a developer
working on the "core Lisp" it can be a very big deal.  While it's
theoretically possible to "unload" a library, after you've spent a few
minutes testing, things tend to get very intertwingled, and a restart
is necessary to guarantee you have a clean environment.