[fix] getxattr must return bytes value

This was already broken in v2.0 in 2012!

Author: mxmlnkn

examples/memory.py

@@ -60,7 +60,7 @@ def getxattr(self, path, name, position=0):
         try:
             return attrs[name]
         except KeyError:
-            return ''
+            return b''
 
     def listxattr(self, path):
         attrs = self.files[path].get('attrs', {})