method dispatch bug on incomplete parameterized types / type constructor issue

[vtjnash]

unlike DataTypes, the Array type template is incomplete, which leads to unexpected dispatch:

julia> z{T<:Base.BLAS.BlasFloat}(A::StridedMatrix{T}) = T

julia> let
                  dim=2
                  S=zeros(Complex,dim,dim)
                  @show typeof(S)
                  z(S)
              end
typeof(S) => Array{Complex{T<:Real},2}
Union(Complex{Float64},Complex{Float32})

(code from #4796)

note that we can obtain a similar failure from BitsTypes:

julia> bitstype 64 A{T} <: Real

julia> reinterpret(A{Int}, 1)
A{Int64}(0x0000000000000001)

julia> reinterpret(A{Real}, 1)
A{Real}(0x0000000000000001)

julia> reinterpret(A, 1)
Segmentation fault (core dumped)