Fixes up messages (errors/warnings).
You can now provide a -fixupmessages property
that specifies a regexp, a restrict: directive (either
error or warning), a replace: value to rewrite the
message, and an is: directive that can move a warning
to error or vice versa.
No longer prefixes an error with its file
Previous refactor error
The return must be true if there is a matching
instruction and not negated.