nvidia-current-dev does not cleanly replace mesa-common-dev

[Kip Warner]

After installing nvidia-current-dev because it provides gl.h, I noticed that it did not remove the previously installed mesa-common-dev which provides standard OpenGL headers in the usual place of /usr/include/GL/. The nvidia package instead provides its interfaces in /usr/include/nvidia-current/GL/. That would be fine if it removed / conflicts with the mesa package and symlinked that location to /usr/include/GL/, but it does not.