Merge branch 'es/chain-lint-more'

Improve built-in facility to catch broken &&-chain in the tests.

* es/chain-lint-more:
  chainlint: add test of pathological case which triggered false positive
  chainlint: recognize multi-line quoted strings more robustly
  chainlint: let here-doc and multi-line string commence on same line
  chainlint: recognize multi-line $(...) when command cuddled with "$("
  chainlint: match 'quoted' here-doc tags
  chainlint: match arbitrary here-docs tags rather than hard-coded names