packaging: postinstall_setup.sh no longer chmod's directories and files to 750...

packaging: postinstall_setup.sh no longer chmod's directories and files to 750 if they already have that permission.

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@3479 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534