Patch check should output list of X new checkstyle warnings

check patch says how many new checkstyle warnings there are, but doesn't provide any sane way of finding out what they are.

We should output the first 10 or so of them, as we do for long lines and such, and give a command line flag for folks who want them all.

With this change, I'd be in favor of closing as wontfix/later the remaining proactive cleanup subtasks.