Keep the outbox as a list: a save logs only the sends and trims it made

The sends not yet trimmed were written whole into the links value at
every save, as the numbers heard were: a sender whose receiver is away
or slow saved all its waiting sends again with each new one. They are
now a runtime list {output (its name), seq, payload}, in the order sent,
stored as a list state is (image "0sent" and its changes in the log). A
send is a change of the list with its event; a trim lets the sends go at
once and a failed save brings them back; the host sees the saved ones
(sent_saved). Outputs are named in the items, so a module replaced keeps
them without moving anything; one that lacks or changed an output with
sends left is refused as before. Links stored before (PLK1, PLK2) move
their sends to the list at a start and are stored again without them
(PLK3).

A list field may now hold any bytes (kind 2), unchecked, besides a number
and a UTF-8 text.

Saving 5,000 sends of 16 KB one by one took 84.8 s and left a store of
400 MB; now 0.91 s and 144 MB. 20,000 of 61 bytes: 8.4 s, now 2.9 s.

0 files changed, 0 insertions, 0 deletions