UniformScaling: allow writing generic polynomicals with I.

	julia> p(x) = x^2 - 2x + I
	p (generic function with 1 method)

	julia> p(4)
	9

	julia> p(rand(3,3))
	3x3 Array{Float64,2}:
	  0.386215   -0.22931    0.0859286
	 -0.18856     0.664356  -0.693054
	  0.0600554  -0.361883   0.619314
Merge pull request #6472 from JuliaLang/sk/unifscal

UniformScaling: allow writing generic polynomicals with I.