Passing back error in response request when the neon request dispatch

fails. This leads to an error when a OSD is disconnected, but actually
should result in retrying the request until the OSD recovers (or we
decide to give up).


git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@47 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534