new system release

[Mike McMahon <MMcM at MIT-AI>]

System 68 is now released to the users.  It has been around on a number
of machines for some time anyway, and will make it to the rest soon.
Except for the couple of things noted below, this system is an
accumulation of bug fixes from the previous system.  Please note that
early (and some intermediate) versions of this system have serious
problems and you should make sure you have the latest patches.  At this
moment, that is system 68.9.

New global function, CATCH-ERROR, which is like ERRSET but returns two
values instead of a list.  The first value is the value of the body form
and the second is non-NIL if an error occurs.

CLEAR-UNIBUS-MAP is called directly from LISP-REINITIALIZE, before
SYSTEM-INITIALIZATION-LIST.  Thus things on SYSTEM-INITIALIZATION-LIST
may initialize unibus-map pages.