Merge branch 'refs/heads/t/invalid-ids'

A single patch that was in misc for a while, and two follow up fixups
that were detected after the branch was merged into next.

* refs/heads/t/invalid-ids (cooking for two weeks):
  Makefile: Don't compile with -Wformat-signedness unconditionally.
  aft.c: Use correct format string for error output.
  touch: Refuse to set an invalid image or lyrics ID.