CategoriesExcludeFilter and CategoriesIncludeFilter created.

This is the first of at least a few changes that aim better to support Categories (eg creating the Request with the Filters is needed).

One open issue with this specific change is how best to specify from the command line the included and excluded categories. My current code uses the properties test.categories.include and test.categories.exclude. Are there other examples of JUnit using properties? Is there some naming convention to follow?

I'm sure there'll be lots of other questions, comments, etc (eg does JUnit already have support of Ant-style globbing that this change can just reuse?).