Added some tests to WatchDir and JmxUtils

Also modified maven-compiler-plugin to compile Java 6 as it seems that sources use 1.6 features (@Override on interfaces). I would like to bump this to Java 7, but I do not know if you have compatibility requirements ...

I wanted to write some tests as an exercise. More test are most of the time a good thing, so you might be interested in merging this. I am probably going to write a few more if you are interested in them ...