Fix adopt bug when used with derived Lua classes.
Fix adopt bug when used with derived Lua classes.

This makes sure we find the top level C++ base class, rather than trying
to destroy only the first level base.

Kazade/luabind-deboostified,rpavlik/luabind,mdave88/luabind,rpavlik/luabind,alex85k/luabind,MrApplejuice/luabind,lonski/luabind,galek/luabind-deboostified,alex85k/luabind,plsytj/luabind,decimad/luabind-deboostified,luabind/luabind,luabind/luabind,grafi-tt/luabind,luabind/luabind,rpavlik/luabind,rpavlik/luabind,ltjax/luabind-deboostified,Wohlhabend-Networks/luabind-deboostified,Oberon00/luabind,alex85k/luabind,luabind/luabind,davidar/luabind,rpavlik/luabind,Oberon00/luabind,mapbox/luabind,alex85k/luabind