MRC: fixed a bug that caused OSD assertion failures in response to striped...

MRC: fixed a bug that caused OSD assertion failures in response to striped truncates when insufficient OSDs were available

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@867 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534