Filter _local docs from the _changes feed

A bandaid to filter out _local docs that were introduced into the docids
btree due to bugs.
Rewind on uuid+last_node mismatch

Only use the StartSeq for a shard if we are sure it is a true
descendant of the shard originally seen. This means that the uuid and
last_node fields encoded in the since value must match the shards
current values. If they do not, rewind to 0.

BugzID: 18726