Commit efe3fe9b8c removed the ability for
`single_match` and `single_match_else` to trigger if comments were
present outside of the arms, as those comments would be lost while
rewriting the `match` expression.
This reinstates the lint, but prevents the suggestion from being applied
automatically in the presence of comments by using the `MaybeIncorrect`
applicability. Also, a note is added to the lint message to warn the
user about the need to preserve the comments if acting upon the
suggestion.
