convert luminance back to a float for star fading. fixes #2580
simplify Color4ub::GetLuminance()
Merge pull request #272 from ParagonDevelopmentTeam/sync

Sync
clamp smoke alpha since it can be negative
Fix population indicator
Clamp speedlines alpha
Merge remote-tracking branch 'johnbartholomew/issue-2580'
Merge pull request #281 from ParagonDevelopmentTeam/colorfix

Colorfix, closes #277
Fix alpha opacity, will probaly be backported from pioneer later
Darken atmopshere based on density, use eyenormals to make fog based on density, make land more visible from space
Eyesphere ray was calculated twice..
Merge pull request #283 from ParagonDevelopmentTeam/shaders_from_gaia

New atmosphere (from gaia)
synced..