evolve: support ancestor of orphan split with unrelated changeset in between This is done by searching for roots and heads within the range delimited on both sides by the target revs instead of just within the target revs. Example: o 5 | o 4 | o 3 | | * 2 | | | x 1 |/ o 0 1 is obsoleted by 3 and 5. We are considering the case when 2 gets evolved. Before the change, both roots and heads were [3, 5]. The user was offered a choice between 3 and 5 as the destination. After the change, roots are [3] and heads are [5]. 5 is chosen as the destination.

exchange: deal with empty obscommon The case can happen, we better support it.

topic: compat with tr.changes[b'phases'], it's now a list

topic: fix compatibility issues caused because of change in transaction API In 36f08ae87ef687be53a59bd87376bcfbe4479205 in core mercurial, `_validator` attribute to transaction class was removed and a dict was introduced. It added a `addvalidator()` function to transaction class which can be used to register multiple validator callbacks. This updates the code to use `addvalidator()` when `_validator` attribute is not present.

obsexchange: fallback to simpler request for dumb http server If the http server cannot accept many arguments, avoid sending too large requests (at the cost of more data exchanged). A better solution would be to aggregate contiguous range, but this is a question for later.

obsexchange: swap the 'common' and 'missing' clause

obsdiscovery: avoid considering locally hidden changeset This looks like a dubious optimisation

obsdiscovery: add a test where some common node are hidden This is useful to prevent regression.

tests: use appropriate Python (2 or 3) for dummyssh

evolve: add missing 'of' in message The message refers to the changeset that is currently evolved. Therefore the message needs an additional 'of' to be correct.