topics/transaction: return immediately if we are in the middle of a transaction

topics/ui: signal when an operation entails voiding a topic Typical situations may include: * publish * push (to publishing server) * pull * fold

topics/ui: signal when the topics command creates a new (empty) topic

topics: signal to the end user when a topic has been forgotten Situation is: * we're updating outside an empty topic. * we've cleared topics

topic: add a --topic option to "outgoing" command By symmetry with "push" in the previous changeset.

topic: add a --topic option to "push" command This is symmetrical with --bookmark or --branch; it selects changesets in specified topic as revisions to push.

test-compat: adapt to core change in b90bd9a98c8b Blackbox just got a little more chatty.

readme: update about obslog update and documentation refresh

topic/tuto: be more precise in the top introduction about the publishing server Indeed there is a chapter with a non-publishing one.

topics/tuto: prefer rebase over merge and remove the weird merge attempt

topics/tuto: typo fix and s/multiple/two

topics/tuto: be more complete over the de-orphaning action within a topic

topics/tuto: try to be more precise on why `hg log` output is hairy

topics/tuto: attempt to have a slightly more clear wording