bookmark: add a dedicated pretxnclose-bookmark hook This new hook mirror the newly introduced 'txnclose-bookmark' but can abort the transaction.

bookmark: add a dedicated txnclose-bookmark hook The new 'txnclose-bookmark' hook expose the bookmark movement information stored in 'tr.changes['bookmarks]'. To provide a simple and straightforward hook API to the users, we introduce a new hook called for each bookmark touched. Since a transaction can affect multiple bookmarks, updating the existing 'txnclose' hook to expose that information would be more complex. The data for all moves might not fit in environment variables and iterations over each move would be cumbersome. So the introduction of a new dedicated hook is preferred in this changeset. This does not exclude the addition to the full bookmark information to the existing 'txnclose' in the future to help write more complex hooks.

tweakdefaults: make commands.update.check be `noconflict` This is the second-safest option we have to offer in `updatecheck`, with `abort` being the safest and `linear` being the default. At the sprint we discussed how much `none` and `linear` make us all uncomfortable, and how we'd like to move the default behavior if we can. I'm not sure we can get away with actually changing the out of the box default behavior, but we can at *least* do this. Differential Revision: https://phab.mercurial-scm.org/D1062