Remove uses of .str(), .c_str() and some other methods of SGPath.
Pass SGPath directly where possible, or explicitly convert to the
appropriate 8-bit encoding.
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.
