Bug#656144: hint: "clean" does not properly check arch-specific hints
hint's "clean" action only takes account of source versions when
deciding whether a migration hint has been completed.
For instance, if one has a hint for pushing armhf and s390x packages -
e.g. "force-hint foo/armhf/1.2 foo/s390x/1.2" - then a subsequent "hint
clean" invocation will move the hint below finished, because foo 1.2 is
in testing. This is, at least imho, unhelpful, particularly if one
doesn't notice that the cleaning has taken place before the britney run
in which the hint was intended to take effect.