loginfo_once for Indigo

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Hello. I'm new here. I'm using Indigo and want to use the new function 'rospy.loginfo_once'. So in my own project file which is python, I insert several codes based on the source code of 'loginfo_once' and succeed to implement such function. Now I want to add these codes to my Indigo's rospy.core so that I can use 'rospy.loginfo_once'. However, it doesn't work by just simply putting them into the source code(/opt/ros/indigo/lib/python2.7/dist-packages/rospy/core.py). So I want to ask how to build the source code to activate my own codes.