Merge branch 'maint' into python-work

Merge branch 'maint' into python-work

* maint:
  docs: avoid a footnote, some related rewordings and improvements
  Revert "docs: parallel-tests is not experimental anymore"
  docs: minor cosmetic fixes
  help: improve text about automatically-distributed files
  refactor: split 'usage' subroutine in automake
  tests: fix bug in 'autodist.test'
  maintcheck: extend 'sc_tests_plain_*' checks
  maintcheck: avoid few spurious failures
  check: don't use multi-line coloring for the report
  ansi2knr: deprecate, it will go away in the next major release
  docs: primary/prefix combination "pkglib_PROGRAMS" is now invalid
  docs: replace obsolete @vindex entry with a useful one
  docs: AM_DISTCHECK_CONFIGURE_FLAGS is for corner cases
  parallel-tests: stricter checks on DISABLE_HARD_ERRORS support
  docs: parallel-tests is not experimental anymore
  check: document and test $(TEST_SUITE_LOG) overriding