A clear error message for checkstyle misconfiguration.
Review Request #4176 - Created Aug. 19, 2016 and submitted
Previously if the --configuration option wasn't specified, you'd get an opaque error much further down, in a call to maybe_list. Also: - Updates to a modern version of checkstyle by default. 6.1.1 doesn't support various checks, so standard configs (such as sun's or google's) that you download from checkstyle's site don't work with it. It's better to impose on the very few (if any) repos using java6 than on everyone else. - Fix a text nit in an unrelated readme.
CI passes: https://travis-ci.org/pantsbuild/pants/builds/153440606