[PATCH] gitk: Updated German translation.

This is an update to gitk's German translation against current master of 
gitk.git at git.kernel.org. To my surprise, my submitted patch as of 
2008-05-24 hasn't been applied so far. I'm resending it (rebased on current 
master) in the hope that by now someone will actually commit it and the 
translation goes back to 100%. Thanks a lot!

Christian