phabricator: combine commit messages into the review when folding commits No visible changes here, until an option to enable it is added to `phabsend`. This combines the Differential fields like Arcanist does, rather than simply concatenating the text blocks. Aside from populating everything properly in the web interface, Phabricator fails the review create/update if repeated fields are seen as would happen with simple concatenation. On the flip side, now that the Summary and Test Plan fields can contain data from multiple commits, we can't just join these fields together to determine if an amend is needed. If that were to happen, every single commit in the folded range would get amended with the combined commit message, which seems clearly wrong. Aside from making a minor assumption about the content of the Differential Revision field (it seems they allow some minor variances with spacing), this means that for folded reviews, you can't post it, go to the web page add a missing Test Plan, and then get it added to the commit message by re-posting it. I don't think that's a big deal. Differential Revision: https://phab.mercurial-scm.org/D8309