python3: rename func_name to __name__

What's New In Python 3.0 [1]:

The function attributes named func_X have been renamed to use the __X__ form,
freeing up these names in the function attribute namespace for user-defined
attributes. To wit, func_closure, func_code, func_defaults, func_dict,
func_doc, func_globals, func_name were renamed to __closure__, __code__,
__defaults__, __dict__, __doc__, __globals__, __name__, respectively.

1. https://docs.python.org/3/whatsnew/3.0.html#operators-and-special-methods

Part of #20

Author: ligurio

lib/connpool.py

@@ -136,14 +136,14 @@ def deco(*args, **kwargs):
             except exc_classes as e:
                 if logger is not None:
                     logger.log(retry_log_level,
-                               retry_log_message.format(f=f.func_name, e=e))
+                               retry_log_message.format(f=f.__name__, e=e))
                 gevent.sleep(interval)
                 failures += 1
                 if max_failures is not None \
                         and failures > max_failures:
                     if logger is not None:
                         logger.log(max_failure_log_level,
                                    max_failure_log_message.format(
-                                       f=f.func_name, e=e))
+                                       f=f.__name__, e=e))
                     raise
     return deco