Fixed unnecessary copy in convert

Fixes #65

Author: neveritt

src/Polynomials.jl

@@ -108,6 +108,7 @@ poly(A::Matrix, var::Char) = poly(eig(A)[1], @compat Symbol(var))
 
 include("show.jl") # display polynomials.
 
+convert{T}(::Type{Poly{T}}, p::Poly{T}) = p
 convert{T}(::Type{Poly{T}}, p::Poly) = Poly(convert(Vector{T}, p.a), p.var)
 convert{T, S<:Number}(::Type{Poly{T}}, x::S) = Poly(promote_type(T, S)[x])
 convert{T, S<:Number,n}(::Type{Poly{T}}, x::Array{S,n}) = map(el->convert(Poly{promote_type(T,S)},el),x)

test/runtests.jl

@@ -193,3 +193,9 @@ as = [im, 1, 2]
 bs = [1, 1, 2]
 @test conj(Poly(as)) == Poly(conj(as))
 @test conj(Poly(bs)) == Poly(conj(bs))
+
+## unnecessary copy in convert #65
+p1 = Poly([1,2])
+p2 = convert(Poly{Int64}, p1)
+p2[3] = 3
+@test p1[3] == 3