ObjectDirectory.GetDirectory() should be Public

[Danielku15]

The GetDirectory() method of the ObjectDirectory class is set as internal: https://github.com/mono/ngit/blob/master/NGit/NGit.Storage.File/ObjectDirectory.cs#L151

But it should be public:
http://git.eclipse.org/c/jgit/jgit.git/tree/org.eclipse.jgit/src/org/eclipse/jgit/storage/file/ObjectDirectory.java#n172

Also applies for fileFor(AnyObjectId).

I need this methods for some tasks.

I am currently using this (very very dirty) Workaround:

string path = objectDirectory.ToString();
path = path.Substring(16, path.Length - 17);

ToString() delivers "ObjectDirectory[" + GetDirectory() + "]". That way it's possible to extract the path.