Add var_indices for universal polynomials (Nemocas#2220)

Author: SoongNoonien

src/generic/UnivPoly.jl

@@ -280,6 +280,8 @@ end
 
 var_index(x::UnivPoly) = var_index(data(x))
 
+var_indices(p::UnivPoly) = var_indices(data(p))
+
 function vars(p::UnivPoly{T}) where {T <: RingElement}
    V = vars(data(p))
    S = parent(p)

test/generic/UnivPoly-test.jl

@@ -147,9 +147,13 @@ end
          @test symbols(S) == [:x, :y, :z]
 
          @test length(vars(S())) == 0
+         @test length(var_indices(S())) == 0
          @test vars(x^2 + 2x + 1) == [x]
+         @test var_indices(x^2 + 2x + 1) == [1]
          @test vars(x*y + 1) == [x, y]
+         @test var_indices(x*y + 1) == [1, 2]
          @test vars(x*y + z) == [x, y, z]
+         @test var_indices(x*y + z) == [1, 2, 3]
 
          @test internal_ordering(S) == ord
       end