Merge branch 'dl/test-must-fail-fixes-3'

Test clean-up continues. * dl/test-must-fail-fixes-3: t5801: teach compare_refs() to accept ! t5612: stop losing return codes of git commands t5612: don't use `test_must_fail test_cmp` t5607: reorder `nongit test_must_fail` t5550: simplify no matching line check t5512: stop losing return codes of git commands t5512: stop losing git exit code in here-docs t5512: don't use `test_must_fail test_cmp`