Update tests and scripts to avoid "test ... -a ...", which is often
more error-prone than "test ... && test ...".

Squashed misconversion fix-up into git-submodule.sh updates.

* ep/avoid-test-a-o:
  git-submodule.sh: avoid "echo" path-like values
  git-submodule.sh: avoid "test <cond> -a/-o <cond>"
  t/test-lib-functions.sh: avoid "test <cond> -a/-o <cond>"
  t/t9814-git-p4-rename.sh: avoid "test <cond> -a/-o <cond>"
  t/t5538-push-shallow.sh: avoid "test <cond> -a/-o <cond>"
  t/t5403-post-checkout-hook.sh: avoid "test <cond> -a/-o <cond>"
  t/t5000-tar-tree.sh: avoid "test <cond> -a/-o <cond>"
  t/t4102-apply-rename.sh: avoid "test <cond> -a/-o <cond>"
  t/t0026-eol-config.sh: avoid "test <cond> -a/-o <cond>"
  t/t0025-crlf-auto.sh: avoid "test <cond> -a/-o <cond>"
  t/lib-httpd.sh: avoid "test <cond> -a/-o <cond>"
  git-rebase--interactive.sh: avoid "test <cond> -a/-o <cond>"
  git-mergetool.sh: avoid "test <cond> -a/-o <cond>"
  git-bisect.sh: avoid "test <cond> -a/-o <cond>"
  contrib/examples/git-resolve.sh: avoid "test <cond> -a/-o <cond>"
  contrib/examples/git-repack.sh: avoid "test <cond> -a/-o <cond>"
  contrib/examples/git-merge.sh: avoid "test <cond> -a/-o <cond>"
  contrib/examples/git-commit.sh: avoid "test <cond> -a/-o <cond>"
  contrib/examples/git-clone.sh: avoid "test <cond> -a/-o <cond>"
  check_bindir: avoid "test <cond> -a/-o <cond>"