auth: the correct prefixes for python bcrypt are $2a or $2b.

handle the 2b too for consistency.

rhodecode/lib/auth.py

@@ -138,7 +138,7 b' class _RhodeCodeCryptoBase(object):'
 
 
 class _RhodeCodeCryptoBCrypt(_RhodeCodeCryptoBase):
-    ENC_PREF = '$2a$10'
+    ENC_PREF = ('$2a$10', '$2b$10')
 
     def hash_create(self, str_):
         self._assert_bytes(str_)