support true scalar functions

src/function.jl

@@ -389,7 +389,7 @@ vtk_append!(vtkfile, f::FeFunction, ::DP1) =
 
 function save_csv(path, f::FeFunction)
     f.space.element::P1
-    f.space.size == (1,) ||
+    prod(f.space.size) == 1 ||
 	throw(ArgumentError("non-scalar functions unsupported"))
     mesh = f.space.mesh
     df = DataFrame()