match: remove match.never Only one user, can be translated to match.exact()

walk: use match.bad callback for filetype messages

match: ignore return of match.bad All users returned false, return can now be dropped

add: use match.bad callback more effectively

match: document bad callback semantics

walk: simplify logic for badfn clause - matchfn redundant - call badfn always rather than fwarn - use for/else rather than keep var