interface: Added optional, redundant XAttr field "value_bytes" which preserves...

interface: Added optional, redundant XAttr field "value_bytes" which preserves binary extended attribute values (if stored in the string "value", protobuf did corrupt these values when parsing/serializing the string).

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@2881 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534