Make north arrow decoration follow map rotation

Closes http://hub.qgis.org/issues/11818

Author: Sandro Santilli

src/app/qgsdecorationnortharrow.cpp

@@ -292,5 +292,8 @@ bool QgsDecorationNorthArrow::calculateNorthDirection()
       mRotationInt = 0;
     }
   }
+
+  mRotationInt += mapCanvas->mapSettings().rotation();
+
   return goodDirn;
 }