Make the sanity bot complain for overlong commit messages

Any commit message exceeding 72 columns is going to be wrapped by Gerrit.

Unfortunately the sanity bot only complains if the text exceeds ... well, more than that, resulting in commits for which the text is wrapped but that receive no complaints from the bot.

I'd suggest the bot to always complain in case a line is overlong. Bonus points if one can find a syntax to allow blockquoting (of compile errors, long urls, etc.) without triggering the bot, but I'm not really sure it's necessary.