Fix registration of custom logging level names.

We have been registering our custom level names ("BLATHER", "TRACE) in the
wrong order since 2004.  Before Python 3.4, the stdlib ``logging`` module
masked the error by registering them in *both* directions.

CHANGES.rst

@@ -5,6 +5,12 @@
 4.1.0 (unreleased)
 ==================
 
+- Fix registration of custom logging level names ("BLATHER", "TRACE).
+
+  We have been registering them in the wrong order since 2004.  Before
+  Python 3.4, the stdlib ``logging`` module masked the error by registering
+  them in *both* directions.
+
 - Add support for Python 3.4.
 
 - Fix POSKeyError during transaction.commit when after savepoint.rollback.

src/ZODB/loglevels.py

@@ -43,5 +43,5 @@ __all__ = ["BLATHER", "TRACE"]
 
 BLATHER = 15
 TRACE = 5
-logging.addLevelName("BLATHER", BLATHER)
-logging.addLevelName("TRACE", TRACE)
+logging.addLevelName(BLATHER, "BLATHER")
+logging.addLevelName(TRACE, "TRACE")