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".
$ hg init
$ echo a > a
$ hg ci -Am t
adding a
$ hg mv a b
$ hg ci -Am t1
$ hg debugrename b
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3
$ hg mv b a
$ hg ci -Am t2
$ hg debugrename a
a renamed from b:37d9b5d994eab34eda9c16b195ace52c7b129980
$ hg debugrename --rev 1 b
b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3