[bug#67841] [PATCH] Clarify error messages for misuse of m4_warn and --help for -W.

[Karl Berry]

Hi Zack,

    Since this touches code shared between Autoconf and Automake, I'm not
    checking it in yet and I'm requesting comments from both sides of the
    fence.

Well, it seems good to me in principle, FWIW. I don't think this
directly affects automake? I admit I did not try to extract the parts
for automake and run the am tests ... --thanks, karl.