Merge branch 'da/mergetool-tests'

The clean-up of this test script was long overdue and is a very welcome change. * da/mergetool-tests: test-lib-functions: adjust style to match CodingGuidelines t7610-mergetool: use test_config to isolate tests t7610-mergetool: add missing && and remove commented-out code t7610-mergetool: use tabs instead of a mix of tabs and spaces