[osg-users] Slave camera lighting with disabled main camera

[Robert Osfield]

Hi Ravi,

Oh well.  I've removed the LightingMode changes, there is a little
clean up in there so I've merged this with master.

FYI, LightingMode is really just there for convince and backwards
compatibility back to the 1.0/2,0 days of the OSG.

These days I'd write lighting management all myself rather than
leverage these built-in defaults.

Robert.