servers: Fixed blocking issue when shutting down an MRC/OSD before having shut...

servers: Fixed blocking issue when shutting down an MRC/OSD before having shut down the DIR. The HeartbeatThread now performs retries only when initially connecting to the DIR; Initial redirects no longer count as retries.

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@2828 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534