Avoid modifying plugin cache inside a mac bundle
It is not ok to modify any file within the mac application bundle, because since the new signature format, any change will invalidate this signature.
After discussion on IRC, a clean solution would be to generate the plugin cache, and sign it as well, as it should not change afterwards.
Current problem is still that the (same) cache gets overwritten again when VLC is started (old file gets deleted and a new file is written). This removes the signature from this file, which has been stored in extended attributes.