Merge branch 'jk/test-chain-lint'

Merge branch 'jk/test-chain-lint'

People often forget to chain the commands in their test together
with &&, leaving a failure from an earlier command in the test go
unnoticed.  The new GIT_TEST_CHAIN_LINT mechanism allows you to
catch such a mistake more easily.

* jk/test-chain-lint: (36 commits)
  t9001: drop save_confirm helper
  t0020: use test_* helpers instead of hand-rolled messages
  t: simplify loop exit-code status variables
  t: fix some trivial cases of ignored exit codes in loops
  t7701: fix ignored exit code inside loop
  t3305: fix ignored exit code inside loop
  t0020: fix ignored exit code inside loops
  perf-lib: fix ignored exit code inside loop
  t6039: fix broken && chain
  t9158, t9161: fix broken &&-chain in git-svn tests
  t9104: fix test for following larger parents
  t4104: drop hand-rolled error reporting
  t0005: fix broken &&-chains
  t7004: fix embedded single-quotes
  t0050: appease --chain-lint
  t9001: use test_when_finished
  t4117: use modern test_* helpers
  t6034: use modern test_* helpers
  t1301: use modern test_* helpers
  t0020: use modern test_* helpers
  ...