Merge branch 'ab/tap'

Merge branch 'ab/tap'

* ab/tap:
  t/README: document more test helpers
  t/README: proposed rewording...
  t/README: Document the do's and don'ts of tests
  t/README: Add a section about skipping tests
  t/README: Document test_expect_code
  t/README: Document test_external*
  t/README: Document the prereq functions, and 3-arg test_*
  t/README: Typo: paralell -> parallel
  t/README: The trash is in 't/trash directory.$name'
  t/t9700/test.pl: don't access private object members, use public access methods
  t9700: Use Test::More->builder, not $Test::Builder::Test
  tests: Say "pass" rather than "ok" on empty lines for TAP
  tests: Skip tests in a way that makes sense under TAP
  test-lib: output a newline before "ok" under a TAP harness
  test-lib: Make the test_external_* functions TAP-aware
  test-lib: Adjust output to be valid TAP format