* lots of bug fixes for MRC and OSD

* more checks of arguments and better error messages in the MRC
* implemented setattr operation in MRC
* new service_get_by_name for the DIR
* replaced KeyValuePairSet with Map

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@227 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534