When cleaning up Caches, do not complain about missing files, thanks to Moritz Lenz!

Squashed commit of the following:

commit 26ec85c8f90bb167060542562278d667b7682647
Author: Moritz Lenz <mlenz@noris.net>
Date:   Wed Sep 4 09:40:16 2013 +0200

    When cleaning up Caches, do not complain about missing files

    it is not really an error, and can occur when another process concurrently
    deleted files