Curve cleanup

Renamed BevPoint's members
* x,y,z -> vec[3]; compatible with other functions.
* f1 -> split_tag; used by displist to set the splitting flag.
* f2 -> dupe_tag; used in curve.c to remove duplicates.

BevList
* flag -> dupe_nr; was being used as a counter for duplicate points.

* use arithb.c functions where possible.

* arrays for coords, tilt and radius were being allocated, then copied into the BevPoint's, now write directly into the values without allocing/freeing arrays.

source/blender/python/api2_2x/Geometry.c

@@ -509,7 +509,7 @@ static PyObject *M_Geometry_BezierInterp( PyObject * self, PyObject * args )
 	
 	coord_array = MEM_callocN(dims * (resolu) * sizeof(float), "BezierInterp");
 	for(i=0; i<dims; i++) {
-		forward_diff_bezier(k1[i], h1[i], h2[i], k2[i], coord_array+i, resolu-1, dims);
+		forward_diff_bezier(k1[i], h1[i], h2[i], k2[i], coord_array+i, resolu-1, dims*sizeof(float));
 	}
 	
 	list= PyList_New(resolu);