fix pubkey for python3.x

pubs/bibstruct.py

@@ -1,4 +1,11 @@
 from __future__ import unicode_literals
+try :
+    import __builtin__
+except: 
+    # Python 3.x
+    import builtins
+    if 'unicode' not in builtins.__dict__.keys():
+        unicode = str
 
 import unicodedata
 import re
@@ -6,6 +13,7 @@ from string import Formatter
 
 from .p3 import ustr, uchr
 
+
 # Citekey stuff
 
 TYPE_KEY = 'type'