Merge branch 'fs/test-prereq'

The test framework learns to list unsatisfied test prerequisites,
and optionally error out when prerequisites that are expected to be
satisfied are not.

* fs/test-prereq:
  test-lib: make BAIL_OUT() work in tests and prereq
  test-lib: introduce required prereq for test runs
  test-lib: show missing prereq summary

diff --cc t/test-lib.sh
Simple merge