For all source directories outside of simgear/scene,
which really depends very hard on osg, avoid using osg
classes. This should reenable the use of some basic and
scenegraph independent parts of simgear without the
the need for osg.
fgpanel is basically the stripped down 2D-Panel code from
FlightGear. It is designed as a standalone lightweight panel
rendering engine to draw 2d panels on a lowcost computer/graphic card
without 3d acceleration at reasonablel framerates.
Patches for inclusion into the build system will follow.
