[vsync] ensure we don't set or show VSYNC_DRIVER on those systems that don't support it. Only show or set on Linux and FreeBSD.
[vsync] switch default in settings.xml to something supported on all systems (ALWAYS) and quirk it on Linux and FreeBSD
Merge pull request #4463 from jmarshallnz/osx_vsync_always

[osx] vsync should default to always