client: Update the cached file size of the xtcl pseudo file by stat()ing it...

client: Update the cached file size of the xtcl pseudo file by stat()ing it instead of reopening it. Fixes issue 234.

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@2819 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534