1) just detect no gif support in GD and turn off the GIF output. I
don't like this because I don't like the way some autoconf based
programs enable and disable user visible features based on what it finds
on your system. Thats why PCB will spit out a message saying "your GD
doesn't support this, if you still want to continue, you need to add
--disable-gif" That way you have explicitly acknowledged that you are
not going to get GIF support and you know why.
2) never support gif output. This also seemed lame.
Maybe what I need to do is detect your strange condition where
--disable-gif && --disable-jpeg && --disable-png are all listed and then
try and take out the png HID entirely.