Patch Set 5: I would prefer that you didn't submit this

I think we should put the cache completely to JGit. In my opinion it belongs to the JGit Repository class.

In EGit we make use of the JGit API commands in package org.eclipse.jgit.api. The EGit Track Operation will soon just call an "Add"-command in this JGit API. Now this "Add"-Command will have to know the ignored resources.