revlog: replace the old `revlog_kind` approach with the new `target` one The new `target` attribute supersedes the previous one. Differential Revision: https://phab.mercurial-scm.org/D10353

revlog: introduce an explicit tracking of what the revlog is about Since the dawn of time, people have been forced to rely to lossy introspection of the index filename to determine what the purpose and role of the revlog they encounter is. This is hacky, error prone, inflexible, abstraction-leaky, <insert-your-own-complaints-here>. In f63299ee7e4d Raphaël introduced a new attribute to track this information: `revlog_kind`. However it is initialized in an odd place and various instances end up not having it set. In addition is only tracking some of the information we end up having to introspect in various pieces of code. So we add a new attribute that holds more data and is more strictly enforced. This work is done in collaboration with Raphaël. The `revlog_kind` one will be removed/adapted in the next changeset. We expect to be able to clean up various existing piece of code and to simplify coming work around the newer revlog format. Differential Revision: https://phab.mercurial-scm.org/D10352

config: add --source option to include source of value Showing the source of each config option is quite useful and not something the user should have to reach for the `--debug` flag for. I updates documentation and tests, except for one place in `test-hgrc.t` where I thought the test might have been intended to also test that `--debug` results in `ui.quiet` etc being test. Differential Revision: https://phab.mercurial-scm.org/D10668