[Automake-NG] [FYI] Merge branch 'master' into ng/master

[Stefano Lattarini]

Merge branch 'master' into ng/master

    * master:
      tests: fix automatic re-execution of tests with Zsh
      tests: drop support for older Zsh shells
      tests: allow AM_TEST_RUNNER_SHELL to be overridden
      tests: fix setup for older Zsh
      missing: do not touch timestamps; only warn for out-of-date files

Signed-off-by: Stefano Lattarini <stefano.lattar...@gmail.com>