capabilities: changed default validity to 48 hours - will be changed back to...

capabilities: changed default validity to 48 hours - will be changed back to 10 mins as soon as the client can renew capabilities

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@690 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534