backout: correct commit status of no changes made (BC) (issue4190)
If backout generated no changes to commit, it showed wrong status, "changeset
<target> backs out changeset <target>", and raised TypeError with -v option.
This changes the return code to 1, which is the same as "hg commit" and
"hg rebase".
To run the tests, do:
cd tests/
python run-tests.py
See http://mercurial.selenic.com/wiki/WritingTests for
more information on writing tests.