rust-changelog: introducing an intermediate `ChangelogEntry` Before this change, client code needing to extract, e.g, the Node ID and the description from a changeset had no other choice than calling both `entry_for_rev()` and `data_for_rev()`. This duplicates some (limited) computation, and more importantly imposes bad hygiene for client code: at some point of developement, the client code would have to pass over both entry and data in its internal layers, which at some point of development would raise the question whether they are consistent. We introduce the intermediate `ChangelogEntry` from which both conversion to the generic `RevlogEntry` and extraction of `ChangelogRevisionData` are possible. It might grow some convenience methods in the future. We keep the `data_for_rev()` method of `Changelog` for compatibility, pointing users at the more powerful alternative.

rust-changelog: added a test for `NULL_REVISION` special case The result is due to `Revlog.get_rev_data()` returning an empty byte string for `NULL_REVISION`, followed by special case for emtpty byte strings in `ChangelogRevisionData::new()`.

rust-changelog: made doc-comments more consistent The most important is the one about `data_for_rev`, that looked like a copy-paste leftover (got me confused first time I read this code, before I actually learned there were both `Entry` and RevisionData`. In the comment for the `struct`, "changelog" was probably more about the format in general (as documented elsewhere) than as an identifier. Some of the "Return something" had "of", half had "for".

commands: correct documentation of hg serve’s --ipv6 option When the --ipv6 option is given, the server doesn’t listen to a IPv4 socket. This can be verified by running two servers, one with and one without the option, which works fine. I think that listening to both a IPv4 and a IPv6 socket would be better, but given that the Python standard library class underlying the HTTP server supports only one socket, this is not trivial.

rhg: don't crash on empty directory names in path_encode, just in case I don't expect that to be possible, but there's nothing in path_encode.rs that prevents it, and the old code didn't crash in this case, so it's better to be defensive.

rhg: fix a bug in path encoding, demonstrated in the parent commit

rhg: show a bug in the rust implementation of path_encode introduced recently In commit 96d31efd21f7 I did a refactoring where I dropped a chunk of code by accident, thus introducing a bug. This commit adds a test demonstrating that bug.

extras: re-use Projection from jaraco.collections

extras: expose 'retained_extras' for extensions to extend

extras: extract function for projecting names from a gettable object