Make deprecated promote_eltype_op type stable

Author: TotalVerb

base/deprecated.jl

@@ -1497,7 +1497,7 @@ function frexp{T<:AbstractFloat}(A::Array{T})
 end
 
 # Calling promote_op is likely a bad idea, so deprecate its convenience wrapper promote_eltype_op
-@deprecate promote_eltype_op(op, As...) promote_op(op, map(eltype, As)...)
+@deprecate promote_eltype_op(op, As...) promote_op(op, Base.eltypes(As...).parameters...)
 
 function unsafe_wrap(::Type{String}, p::Union{Ptr{UInt8},Ptr{Int8}}, len::Integer, own::Bool=false)
     Base.depwarn("unsafe_wrap(String, ...) is deprecated; use `unsafe_string` instead.", :unsafe_wrap)