Two tests looked for "[Uu]sage" in the output, but we cannot expect the
l10n to use that phrase. Mark them with test_i18ngrep so that in later
versions we can test truly localized versions with the same tests, not
just GETTEXT_POISON that happens to keep the original string in the
output.
Merge a few tests that were artificially split into "do" and "test output
under C_LOCALE_OUTPUT" in the original i18n patches back.