filemerge: set default labels a little earlier
By setting the default labels a little earlier, we can rely on them
always being set, as far as I can tell. It may actually even be fine
to rely on that even if we don't set them earlier, but it makes more
sense to me to do it.
Differential Revision: https://phab.mercurial-scm.org/D12015
$ hg init
$ touch unknown
$ touch a
$ hg add a
$ hg ci -m "1"
$ touch b
$ hg add b
$ hg ci -m "2"
Should show unknown
$ hg status
? unknown
$ hg revert -r 0 --all
removing b
Should show unknown and b removed
$ hg status
R b
? unknown
Should show a and unknown
$ ls -A
.hg
a
unknown