phases: fix advanceboundary behavior when targetphase !=0
Changeset was properly removed from upper phase but was not explicitly added to
target phase. If advanced changesets had not pwasnt in target phase they was
considered public (0-phase).
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls
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