tests: stabilise mq rebase tests Prepare for including hashes in output ... and less globbing make the tests easier to update.

test-graft: use strip extension instead of mq extension It only needs strip, no reason to load all of mq.

transaction: remove the 'onabort' mechanism It has no known users. If someones needs similar functionality, a new 'addabort' method similar to 'addfinalize' should be added.

transaction: remove the redundant 'onclose' mechanism It is superseded by the 'addfinalize' function and all its user have been migrated.

fncache: document the fact fncache is outdate at hook run time Using 'addfinalize' to generate 'fncache' means that no pending version of the file will be generated for the hooks. We would have to use the 'addfilegenerator' method to get such result. However the 'fncachevfs' (who decide that a write is necessary) have no access to the transaction to register such file generation at add time. Having the transaction accessible to the 'vfs' is too much trouble for no benefit. This outdated 'fncache' file at hook time is not expected to be an issue. The previous move from 'onclose' to 'addfinalize' had no impact on this timing. I'm documenting it now because I looked at it.

fncache: drop dedicated 'onclose' function in favor of 'tr.addfinalize' Now that we have a shiny generic mechanism, we can use it.

merge with stable

graft: drop cset description from empty commit message This is either already redundant in the output or too verbose in quiet mode.

graft: show hashes in user-facing messages Graft was in various places just showing the revision number in status messges. Instead, also show the stable and more useful short hash.

graft: give helpful warning for empty grafts It was just showing a status message with the internal revision number. Instead, show a warning like note: graft of 27:3aaa8b6725f0 "28" created no changes to commit (message tweaked in-flight by mpm)