tests: new test for mq qdiff command
`hg qdiff .' is supposed to work but it is currently broken.
This test should help us verify when it gets fixed.
(the addremove command is deprecated; use add and remove --after instead)adding dir/baradding foodir/barfoo(the addremove command is deprecated; use add and remove --after instead)adding dir/bar_2adding foo_2dir/bar_2foo_2