client: Fixed error "--striping-policy, --striping-policy-width or...

client: Fixed error "--striping-policy, --striping-policy-width or --striping-policy-stripe-size are only allowed in conjunction with --set-dsp" in xtfsutil introduced in revision 2723.

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@2726 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534