contrib: Additional read method in HDFS interface. Buffersize while...

contrib: Additional read method in HDFS interface. Buffersize while reading/writing to HDFS can now be configured. Updated user guide appropriately.

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@2939 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534