tests: make 'saved backup' globbing less narrow in rebase tests Globbing the hash made it harder to maintain tests with run-tests -i when it was so far by the generated test output. The hashes are stable and we just need to add a (glob).

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transaction: remove the redundant 'onclose' mechanism It is superseded by the 'addfinalize' function and all its user have been migrated.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 This outdated 'fncache' file at hook time is not expected to be an issue.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.