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

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`