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