import the upstream absolute filename fix, closes #12

This is a patch found in the upstream OpenNI2 sources, from after our branch was created. In the patch, I've left a reference to the actual commit that I pulled this patch from.

I've built a debian, installed on 12.04, and tested that my installed openni2_camera works against it with Asus Xtion Pro Live, Primesense 1.082 and Primesense 1.09.