Add a shell script to run all tests from the command-line

This script is also meant for use with ‘git bisect run’ to help
developers track down regressions.
Mention using run-tests.sh with ‘git bisect run’ in the README
Merge branch 'test-shell-script'

* test-shell-script:
  Mention using run-tests.sh with ‘git bisect run’ in the README
  Add a shell script to run all tests from the command-line