MBS-6331: When editing areas, check for duplicate ISO codes
MBS-6331: Simplify test code by inlining some variables
MBS-6331: Remove find_by_iso_3166_1_code in favour of get_by_iso_3166_1
Merge branch 'master' into mbs-6331

Conflicts:
	t/lib/t/MusicBrainz/Server/Data/Area.pm
MBS-6350: Merge release events on release merges

If one release has a release event for a certain date and a country,
and another release has a release event for the same date but without
a country, then the release event without a country should be entirely
discarded.
Merge branch 'mbs-6331' into beta
Merge branch 'mbs-6350' into beta