[Opensg-core] Make recurse* member funcs of StageHandlerMixin public?

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

	Hi Gerrit,

I was just fixing a typo in the fcd templates and wondering why the test 
container stuff had not caught it, when I realized that they can not be 
built ATM (at least not with the regular build system code). While 
fixing that I ran into the following compiler error:

Source/Test/GroupLib/OSGRenderActionTestInit.cpp:202: 
recurseNoNodeCallbacks is protected in this context.

Normally this is solved now by calling a function of the 
StageHandlerMixin (recurseFromThis probably?), but that can only be done 
from callbacks that are member functions of the stage container, not 
from e.g. a free function.
Should we make the recurse* members of StageHandlerMixin public?

	Thanks,
		Carsten