Add support for Python 3

Add support for running under Python 3, while maintaining compatibility
with Python 2.

See http://python-future.org/compatible_idioms.html for more details
behind these changes.

wa/utils/log.py

@@ -128,13 +128,13 @@ def disable(logs):
 
 
 def __enable_logger(logger):
-    if isinstance(logger, basestring):
+    if isinstance(logger, str):
         logger = logging.getLogger(logger)
     logger.propagate = True
 
 
 def __disable_logger(logger):
-    if isinstance(logger, basestring):
+    if isinstance(logger, str):
         logger = logging.getLogger(logger)
     logger.propagate = False