phases: apply similar early filtering to advanceboundary
advanceboundary is called the push's unbundle (but not the other unbundle) so
advanceboundary did not show up the profile I looked at so far.
We start with simple pre-filtering to avoid doing any work if we don't needs
too.
$ hg init repo
$ cd repo
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls -A
.hg
a
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
B should disappear
$ ls -A
.hg
a