Merge branch 'ab/keep-git-exit-codes-in-tests'

Merge branch 'ab/keep-git-exit-codes-in-tests'

Updates tests around the use of "test $(git cmd) = constant".

* ab/keep-git-exit-codes-in-tests:
  rev-list simplify tests: don't ignore "git" exit code
  checkout tests: don't ignore "git <cmd>" exit code
  apply tests: don't ignore "git ls-files" exit code, drop sub-shell
  gettext tests: don't ignore "test-tool regex" exit code
  rev-list tests: don't hide abort() in "test_expect_failure"
  diff tests: don't ignore "git rev-list" exit code
  notes tests: don't ignore "git" exit code
  rev-parse tests: don't ignore "git reflog" exit code
  merge tests: use "test_must_fail" instead of ad-hoc pattern
  apply tests: use "test_must_fail" instead of ad-hoc pattern
  diff tests: don't ignore "git diff" exit code in "read" loop
  diff tests: don't ignore "git diff" exit code
  read-tree tests: check "diff-files" exit code on failure
  tests: use "test_stdout_line_count", not "test $(git [...] | wc -l)"
  tests: change some 'test $(git) = "x"' to test_cmp