Minor mod needed to Coral %stack-block walker template patch

[Dan Rabin <rabin@arisia.Xerox.COM>]

The following will interest users of PCL in Coral (Allegro)
Common Lisp 1.2.1 or 1.2.2 for the Macintosh:

Symptom: compilation of ccl:rlet within pcl:with-slots fails.
Fix:

In Cinco de Mayo PCL as it was retrievable from Arisia on 18 May,
the file walk.lisp contains

#+Coral
(define-walker-template ccl:%stack-block walk-let)

This should be changed to

#+:Coral
...

for the reason that Coral Common Lisp does not coerce
conditional-read feature-names to the keyword package.

--Dan Rabin