md5(1): honor the locale when encoding filenames

[nick_spun.io]

Summary

We weren't calling setlocale() so safename() was unnecessarily escaping characters regardless of the user's set locale

PR: 295875

(Not sure if the test is really necessary here)

Test Plan

test suites run successfully, new test added

[emaste]

Please generate patches with -U999999 to include full context (if you have an update for this review).

[nick_spun.io]

Further issues from the safename() change at D56615 popped up at the same PR here https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=295875