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

# Balto (https://bitbucket.org/lothiraldan/balto/src) is a test orchestrator
# which is compatible with all test runner that can emit the LITF
# (https://github.com/lothiraldan/litf) test format.

# The plugin for the Mercurial test runner is mercurial-litf
# (https://pypi.org/project/mercurial-litf/). Make sure to follow the
# instruction and configuration instructions here:
# https://bitbucket.org/lothiraldan/mercurial_litf/src/default/

# You can launch Balto with `balto /path/to/mercurial/tests/`

name = "Mercurial Test Suite"
tool = "mercurial"