Updates the Checkstyle core version to 6.4.1

Please note that this version requires Java 7 as the minimum runtime environment. This requires you to run Eclipse on a Java 7 (or newer) JVM in order to use this plugin version.

This restriction does not affect the ability to analyze Java 5 or lower level source code.

Please further note that with Checkstyle 6.2 the StrictDuplicate and RedundantThrows check have been removed without replacement.
Also the configuration option ignoreDirectoryName of the PackageDeclaration checks has been removed.
If your Checkstyle configuration uses one of those checks/options adaptations will be required in order to use your configuration with this version.
Please read the Checkstyle release notes for details.

Bugfixes