Merge branch 'warns-win-over-strictness'

Merge branch 'warns-win-over-strictness'

* warns-win-over-strictness:
  Update docs w.r.t. warning and strictness options.
  More tests on warnings/strictness precedence.
  Update NEWS about the warnings-over-strictness precedence.
  Warnings win over strictness in AUTOMAKE_OPTIONS.
  Change signature of 'Automake::Options::_process_option_list()'.
  Add more tests about AUTOMAKE_OPTIONS.
  Warnings win over strictness in AM_INIT_AUTOMAKE.
  Warnings win over strictness on command line.
  More tests on warnings and strictness.
  New test on silent-rules mode and portability warnings.
  Add new tests on strictness and warnings precedence and overriding.