test: add a push race case where each client replaces a different head We check case where the raced push replace one head while the racing push replaces another unrelated one. That second test also make sure we synchronise all repositories to the same state between tests. That will help us when allowing some sort of concurrent pushes.

test: add a file dedicated to push race between clients There are very few tests around the detection of push race. This file will be dedicated to covering these cases more through fully. We start with a simple case. More complex cases get added in later changesets. My end goal here is to provide a way for server to accept concurrent push as long as they are not touching the same heads. However, I want to buff the test coverage of that code before touching anything.

strip: strip obsmarkers exclusive to the stripped changeset This is it, `hg strip --rev X` will now also remove obsolescence markers exclusive to X. Since a previous changeset, the obsmarkers has been backed up in the strip backup bundle, so it is possible to restore them. Note: stripping obsmarkers means the precursors of the stripped changeset might no longer be obsolete after the strip. Stripping changeset without obsmarkers can be useful when building test case. So It is possible to disable the stripping of obsmarkers using the 'devel.strip-obsmarkers' config option. Test change have been carefully validated.