[osx] - add function for identifying osx snow leopard runtime
[settings] - add settingscondition OsxIsSnowLeopard
[osx/settings] - make the fake fullscreen option only visible when running
on snowleopard - it leads to black screen on all later osx versions
Merge pull request #4894 from Memphiz/osxfakefullscreen

[osx] - only show the fake fullscreen option on snow leopard