Merge branch 'sb/dashless'

* sb/dashless: Make usage strings dash-less t/: Use "test_must_fail git" instead of "! git" t/test-lib.sh: exit with small negagive int is ok with test_must_fail Conflicts: builtin-blame.c builtin-mailinfo.c builtin-mailsplit.c builtin-shortlog.c git-am.sh t/t4150-am.sh t/t4200-rerere.sh