MRC: added info about requestor's and owner's uids in case 'access denied' is...

MRC: added info about requestor's and owner's uids in case 'access denied' is reported when invoking an operation

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@1117 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534