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