client: separated entry bookkeeping data from Stat objects for the StatCache;...

client: separated entry bookkeeping data from Stat objects for the StatCache; now able to selectively write-through or write-back attributes

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@1592 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534