Fix missing const in method getThreshold
diff --git a/src/main/include/log4cxx/appenderskeleton.h b/src/main/include/log4cxx/appenderskeleton.h
index 81ca261..3face72 100644
--- a/src/main/include/log4cxx/appenderskeleton.h
+++ b/src/main/include/log4cxx/appenderskeleton.h
@@ -173,7 +173,7 @@
 		Returns this appenders threshold level. See the #setThreshold
 		method for the meaning of this option.
 		*/
-		const LevelPtr& getThreshold()
+		const LevelPtr& getThreshold() const
 		{
 			return threshold;
 		}