MRC: fixed problem w/ default OSD filtering policy, added warning log messages...

MRC: fixed problem w/ default OSD filtering policy, added warning log messages if no OSDs could be assigned to a file or replica

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@1206 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534