Eclipse-CS does not re-run Checkstyle unless I rebuild

[rnveach]

While working on #454 ,

I noticed when I change the configuration file and add a new module, Eclipse-CS did not force a new Checkstyle run and kept the old results in the problem view.

I have the project set to Build Automatically, and even tried turning that off and do a manual build.

It seems Eclipse-CS does not re-run Checkstyle unless I do a clean and rebuild. I can re-save a single file and it will refresh that one file, but that isn't very friendly for the user to do when a project has thousands of files.

I expected Checkstyle to be re-run when I modify a configuration file, when in Eclipse itself as it sees the change occurring.