Cycles Hair: Two basic bair shaders added

A new hair bsdf node, with two closure options, is added. These closures allow the generation of the reflective and transmission components of hair. The node allows control of the highlight colour, roughness and angular shift.

Llimitations include:
-No glint or fresnel adjustments.
-The 'offset' is un-used when triangle primitives are used.

intern/cycles/kernel/kernel_shader.h

@@ -272,7 +272,7 @@ void shader_setup_from_sample(KernelGlobals *kg, ShaderData *sd,
 #ifdef __INSTANCING__
 	sd->object = object;
 #endif
-	/* currently no access to bvh prim index for strand sd->prim - this will cause errors with needs fixing*/
+	/* currently no access to bvh prim index for strand sd->prim*/
 	sd->prim = prim;
 #ifdef __UV__
 	sd->u = u;