merge_people moved a person's faces onto the target and left the
"not this person" rejections on the redirect. A rejection there binds
nothing: once Annie is Anna, the grouping pass is free to suggest the
face the user pushed away from Annie as Anna, which is the behaviour
rejections exist to prevent. The Identity screen's merge has done this
since it was written, and the deduplication job for #78 merges through
the same function, so it would have done it for every same-name pair.
The source's rejections now move to the target (INSERT OR IGNORE, so
one the target already holds is not doubled). Where the two halves
disagree about one face, confirmed as one and rejected as the other,
the confirmation stands, as `confirm` already rules for one face; and a
moved rejection withdraws a suggestion of the same face, as `reject`
already does. Confirmations and names are unchanged.
The body is split into merge_people_within, taking the caller's
transaction, so a job that merges several pairs commits once
(unchecked_transaction cannot nest). merge_people keeps its signature
and its one transaction.
dtourolle
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