Fix up a couple rewrites for features implemented since NGS.
MBS-6735: Allow ProcessReplicationChanges to work with UPDATEs that cross the --limit boundary

There is now a continuation that runs another FETCH on the cursor
that is passed around. If UPDATE needs an extra row that isn't in
the current cursors window, then it can invoke the continuation to
FETCH another n rows.
Change PGQ reindex_caa trigger to only insert if the release exists

If the release doesn't exist the event would still be added, but
it would be invalid (the event body was 0 bytes) which caused the
indexer to become stuck. Now we combine the selection with inserting
the event, so if the release doesn't exist then no event will be created.
Merge branch 'caa-index-trigger' into beta
Merge branch 'mbs-6735' into beta
Merge remote-tracking branch 'ian/rewrites-tweak' into beta