close #215 with @andreasvarga soln

Author: jverzani

src/polynomials/Polynomial.jl

@@ -83,26 +83,27 @@ julia> p.(0:3)
 
 function Base.:+(p1::Polynomial{T}, p2::Polynomial{S}) where {T, S}
     n1, n2 = length(p1), length(p2)
+    R = promote_type(T,S)
     if n1 > 1 && n2 > 1
        p1.var != p2.var && error("Polynomials must have same variable")
        if n1 >= n2
-          c = copy(p1.coeffs)
+          c = R.(copy(p1.coeffs))
           for i = 1:n2
             c[i] += p2.coeffs[i]
           end
         else
-            c = copy(p2.coeffs)
+            c = R.(copy(p2.coeffs))
             for i = 1:n1
               c[i] += p1.coeffs[i]
             end
         end
         return Polynomial(c, p1.var)
     elseif n1 <= 1
-       c = copy(p2.coeffs)
+       c = R.(copy(p2.coeffs))
        c[1] += p1[0]
        return Polynomial(c, p2.var)
     else 
-       c = copy(p1.coeffs)
+       c = R.(copy(p1.coeffs))
        c[1] += p2[0]
        return Polynomial(c, p1.var)
     end

test/StandardBasis.jl

@@ -144,6 +144,13 @@ end
         @test p / 2  == P([1/2, 1.0, 3/2])
         @test p * 0.5 == P([1/2, 1.0, 3/2])
     end
+
+    # ensure  promotion of +,*; issue 215
+    for P in Ps
+        p,q = P([1,2,3]), P(im, :θ)
+        @test p+q == P([1+im, 2, 3])
+        @test p*q == P(im*[1,2,3])
+    end
 end
 
 @testset "Divrem" begin