ancestor.missingancestors: don't discard from basesvisit
We only actually care about whether revsvisit is empty, so we can let
basesvisit grow to arbitrary size.
It turns out that this actually helps performance. For a large repo with
hundreds of thousands of commits, hg perfrevset 'only(0, tip)' (basically the
worst case, involving a full DAG traversal) goes from 1.63 seconds to 1.50. hg
perfrevset 'only(tip, 0)' remains unchanged at 1.98 seconds.
$ hg init
$ echo a > a
$ hg ci -Am0
adding a
$ hg -q clone . foo
$ touch .hg/store/journal
$ echo foo > a
$ hg ci -Am0
abort: abandoned transaction found!
(run 'hg recover' to clean up transaction)
[255]
$ hg recover
rolling back interrupted transaction
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions
Check that zero-size journals are correctly aborted:
#if unix-permissions no-root
$ hg bundle -qa repo.hg
$ chmod -w foo/.hg/store/00changelog.i
$ hg -R foo unbundle repo.hg
adding changesets
abort: Permission denied: $TESTTMP/foo/.hg/store/.00changelog.i-* (glob)
[255]
$ if test -f foo/.hg/store/journal; then echo 'journal exists :-('; fi
#endif