keyword: handle resolve to either parent
Merged files are considered modified at commit time even if only 1 parent
differs. In this case we must use the change context of this parent for
expansion.
The issue went unnoticed for long because it is only apparent until the next
update to the merge revision - except in test-keyword where it was always
staring us in the face.
$ rm -rf a
$ hg init a
$ cd a
$ echo a > a
$ hg ci -Am0
adding a
$ hg tag t1 # 1
$ hg tag --remove t1 # 2
$ hg co 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg tag -f -r0 t1
$ hg tags
tip 3:a49829c4fc11
t1 0:f7b1eb17ad24
$ cd ..