Merge pull request #579 from skgsergio/fix_log_python3.4

Fix AttributeError exception in log.py with python3.4

src/log.py

@@ -208,8 +208,11 @@ class ValidLogLevel(registry.String):
     minimumLevel = -1
     def set(self, s):
         s = s.upper()
+        try:
             try:
                 level = logging._levelNames[s]
+            except AttributeError:
+                level = logging._nameToLevel[s]
         except KeyError:
             try:
                 level = int(s)