Set up the model view matrix exactly as ssg does it before drawing sky, stars

sun, and moon.  I really should do a derived sgLeaf class so that these things
can be drawn within ssgCullandDraw() but this is quicker for now ...

simgear/ephemeris/sky.hxx

@@ -30,6 +30,14 @@
 #endif                                   
 
 
+#include <ssg.h>		// plib include
+
+
+class fgSky : ssgLeaf
+{
+};
+
+
 // (Re)generate the display list
 void fgSkyInit( void );