SceneGraph: workaround ambiguous overloads on deprecated GCC < 4.7 build.

GCC 4.7 cannot detect proper overload based on arguments in initializer
list constructor of some type, thus we need to provide explicit overload
taking std::initializer_lists.
SceneGraph: no need to return void.
SceneGraph: avoid unnecessary copies in deprecated functions.

Optimizations of deprecated API? What the hell am I doing?