bookmarks: actual fix for race condition deleting bookmark This is a simple but efficient fix to prevent the issue tested in `test-bookmarks-corner-case.t`. It might be worth pursuing a more generic approach where filecache learn to depend on each other, but that would not be suitable for stable. The issue is complicated enough that I documented the race and its current solution as inline comment. See this comment for details on the fix.

localrepo: introduce a `_refreshchangelog` method See next changeset for usage and documentation for details.

bookmarks: actually trigger the race deleting bookmark in the test The previous committed version of the test did not triggered the race, but this was hidden by a strange behavior from the test runner. So we are moving the test to a slightly more complex that actually trigger the issue.

test: add some assert in the bookrace extension This cannot hurt to have a bit more security in the test extension.