everyone likes a gross hack now and then!

[Alan Bawden <ALAN at MIT-MC>]

If we are going to have (eq (plist "foo") (plist "bar")), then why not
make stringp be a check to see if the plist of the symbol is eq to the
cannonical one?

If *string-plist* is bound to (+INTERNAL-STRING-MARKER T), then
(stringp x) can macroexpand into (eq (cdr x) *string-plist*), which
should compile just about optimally.  (Of course if you want strings
to have property lists, then this won't work.)