phases: avoid N² behavior in `advanceboundary`
We allowed duplicated entries in the deque, which each entry could potentially
insert all its ancestors. So advancing boundary for the full repository would
mean each revision would walk all its ancestors, resulting in O(N²) iteration.
For repository of any decent size, N² is quickly insane.
We introduce a simple set to avoid this and get back to reasonable performance.
#require unix-permissions no-root
$ hg init a
$ cd a
$ echo foo > b
$ hg add b
$ hg ci -m "b"
$ chmod -w .hg/store
$ cd ..
$ hg clone a b
requesting all changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
new changesets 97310831fa1a
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ chmod +w a/.hg/store # let test clean up
$ cd b
$ hg verify -q
$ cd ..