Unity3 shader: something's changed?

I'm trying to get the Fur shader (from script wiki) working in 3.0. Worked fine in 2.6, partially in 3.0 beta 6, and not at all in beta 7.

I get this error 'expression left of ".fog" is not a struct or array at line ...

code looks like

v2f o;
FurVertexPass (0, v, _FurLength, o.pos, o.fog, o.color, o.uv);

v2f btw defined as

struct v2f {
  V2F_POS_FOG;
  float4 color : COLOR0;
  float4 uv : TEXCOORD0;
};

Apparently V2F_POS_FOG is a built-in thing? According to http://unity3d.com/support/documentation/Manual/ShaderTut2.html

So, has that built-in thing changed? Any ideas how to proceed? (I'm very new to shader programing as you can tell)