Merge branch 'jc/latin-1' into maint

Some platforms no longer understand "latin-1" that is still seen in
the wild in e-mail headers; replace them with "iso-8859-1" that is
more widely known when conversion fails from/to it.

* jc/latin-1:
  utf8: accept "latin-1" as ISO-8859-1
  utf8: refactor code to decide fallback encoding