client: Fixed releasing of locks.

If there are multiple open file handles for a file, only the Close of the last FileHandle releases all active locks. For all other FileHandle::Close() calls the user has to use the new method ReleaseLockOfProcess() to release the locks of his file handle's process on its own in order to ensure the POSIX semantics. The FuseAdapter was adapted to this change.

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@2514 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534