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
#require no-windows
#testcases safe normal
#if safe
$ echo "[format]" >> $HGRCPATH
$ echo "exp-share-safe = True" >> $HGRCPATH
#endif
$ . "$TESTDIR/remotefilelog-library.sh"
$ cat >> $HGRCPATH <<EOF
> [extensions]
> remotefilelog=
> share=
> EOF
$ hg init master
$ cd master
$ cat >> .hg/hgrc <<EOF
> [remotefilelog]
> server=True
> EOF
$ echo x > x
$ hg commit -qAm x
$ cd ..
$ hgcloneshallow ssh://user@dummy/master source --noupdate -q
$ hg share source dest
updating working directory
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg -R dest unshare