[Opensg-core] [OpenSG2] ChangeList::_iSubRefLevel ?

[Carsten N. <car...@gm...>]

	Hi Gerrit,

what is the sub ref level in the changelists, it is counted up and down 
but does not seem to be used?
If it is NIY could you please explain what purpose it is intended to 
serve, so I can try to figure out if and how to use it.

	Thanks,
		Carsten