Fix checkstyle failures on master

The first commit (to checkstyle.xml itself) is just cleanup
Other options here:

* do not add the exclude at this level, but override the plugin config in resources/pom.xml
* use a [suppressions filter](http://maven.apache.org/plugins/maven-checkstyle-plugin/examples/suppressions-filter.html) instead. That would narrow down the exception, but the line numbers would go out of sync pretty quickly as checkstyle.xml is updated, I suspect
* add [`<property name="fileExtension" value="java">`](http://checkstyle.sourceforge.net/config_regexp.html) or so to the `@author` module config. But we probably want to check all files (well, _except_ checkstyle.xml) for this tag

@andrewgaul Thoughts?