Fix IS macro's handling of the default (unknown) case
Fix IS macro's handling of the default (unknown) case

In the list-match-case form we were using _? (which only matches the
symbol _?) instead of ?_ (which matches anything), so the default
clause was never being used.

darcs-hash:20060210095755-dd2a1-a37204ae018b2ad13ca994bd9fcf38ea3deef999.gz

kmizumar/fiveam