[vec] Fix sqrdist* functions.

vec.lua

@@ -148,14 +148,14 @@ end
 function vec.sqrdist(x1,y1, x2,y2)
     local dx,dy = x2-x1, y2-y1
 
-    return dx*dx, dy*dy  -- vec.sqrlen(dx,dy)
+    return dx*dx + dy*dy  -- vec.sqrlen(dx,dy)
 end
 
 --- vec.sqrdist() equivalent for 3D vectors.
 function vec.sqrdist3(x1,y1,z1, x2,y2,z2)
     local dx,dy,dz = x2-x1, y2-y1, z2-z1
 
-    return dx*dx, dy*dy, dz*dz
+    return dx*dx + dy*dy + dz*dz
 end
 
 --- Calculate the distance between two vectors/points.