For duplicate file ids the update phase and reconcile phase determined
the rename mappings independently. If they disagreed (due to different
order of processing), complicated misbehavior would result.
This patch fixes it by letting reconcile try to use the mapping that the
update phase has computed first.
When users share the same tree several times (say A/ and A/B/ are both
shared) the remote tree can have several entries that have the same
file id. This needs to be respected in rename detection.
Also adds several tests and fixes for issues noticed during testing.
See #6096
asapelkin