[FIX] auth_crypt: safer import of base module

Commit 856bc6f2
may cause an issue if the auth_crypt module
is loaded before the base module. That should never
happen in normal circumstances, but forcing an
explicit import does not hurt and makes it safer.

Closes #6742

addons/auth_crypt/auth_crypt.py

@@ -22,7 +22,8 @@ _logger = logging.getLogger(__name__)
 magic_md5 = '$1$'
 magic_sha256 = '$5$'
 
-openerp.addons.base.res.res_users.USER_PRIVATE_FIELDS.append('password_crypt')
+from openerp.addons.base.res import res_users
+res_users.USER_PRIVATE_FIELDS.append('password_crypt')
 
 def gen_salt(length=8, symbols=None):
     if symbols is None: