update accelerator: Don't change owner of ALL files in cache.

update accelerator: Don't change owner of ALL files in cache.

When a file has been downloaded, all files in the update accelerator
cache directory have been chowned which causes huge IO load.
It is only required to set permissions that members of the group
can delete the files (purge function on the web user interface).

Changing the owner is completely unnecessary as only the squid
user needs write access and the web server is able to deliver
any file in the update cache anyways.