Liberapay was originally included using a numeric ID, since they had
not yet finalized the public URLs. Now it is a username. So this
logic prefers the username in Liberapay: field, and keeps the old
LiberapayID: to ease migration. LiberapayID: will not override
Liberapay:. Clients are expected to prefer Liberapay: over LiberapayID:
# Conflicts:
# fdroidserver/update.py
# tests/metadata/info.guardianproject.checkey.yml
# tests/metadata/obb.main.oldversion.yml
# tests/metadata/org.adaway.yml
# tests/update.TestCase