Don't display error message when cancelling login for issue180

tryton/common/common.py

@@ -591,7 +591,7 @@ def process_exception(exception, parent, obj='', method='', *args):
         while True:
             password = ask(_('Password:'), parent, visibility=False)
             if password is None:
-                break
+                raise Exception('NotLogged')
             res = rpc.login(rpc._USERNAME, password, rpc._SOCK.host,
                     rpc._SOCK.port, rpc._DATABASE)
             if res < 0:

tryton/tryton.py

@@ -66,6 +66,10 @@ class TrytonClient(object):
 
         def excepthook(exctyp, value, tb):
             import common
+
+            if str(value) == 'NotLogged':
+                return
+
             tb_s = reduce(lambda x, y: x+y,
                     traceback.format_exception(exctyp, value, tb))
             for path in sys.path: