[Mapserver-dev] Draw line with antialias

[Steve Lime]

This is more for Dan/Assefa: Version 4.0 requires a minimum version of
GD, 2.0.12. With that version antialiasing is available automatically so
there's no need for a GD_USE_ANTIALIAS flag at all. Mapgd.c doesn't use
it and configure won't finish if the GD antialiasing functions aren't
present.

Steve