filemerge: move check for identical sides out of filemerge()
`filemerge.filemerge()` returns `None` if no merge was necessary
because the two sides were identical. I don't think it should be that
function's responsibility to handle that case; we should ideally not
even call `filemerge.filemerge()` if the two inputs identical. This
patch therefore moves the check out to the caller (`mergestate.py`).
The largefiles test changed because we now notice that the two sides
made the same change, so we don't consider it a merge. Also note that
the new message better matches the line above it in the test output.
Differential Revision: https://phab.mercurial-scm.org/D12154
$ hg init repo
$ cd repo
$ echo 0 > a
$ hg ci -qAm 0
$ for i in 5 8 14 43 167; do
> hg up -q 0
> echo $i > a
> hg ci -qm $i
> done
$ cat <<EOF >> .hg/hgrc
> [alias]
> l = log -T '{rev}:{shortest(node,1)}\n'
> EOF
$ hg l
5:00f
4:7ba5d
3:7ba57
2:72
1:9
0:b
$ cat <<EOF >> .hg/hgrc
> [experimental]
> revisions.disambiguatewithin=not 4
> EOF
$ hg l
5:00
4:7ba5d
3:7b
2:72
1:9
0:b
9 was unambiguous and still is
$ hg l -r 9
1:9
7 was ambiguous and still is
$ hg l -r 7
abort: ambiguous revision identifier: 7
[10]
7b is no longer ambiguous
$ hg l -r 7b
3:7b
$ cd ..