make broadcast treat all type arguments as scalars (fix DataArrays.jl#229)

[Sacha0]

Base.Broadcast.broadcast_containertype is incorrect for ::Type{T} arguments to upstream broadcast where T <: Union{Tuple, Ref, AbstractArray, Nullable}, e.g. Base.Broadcast.broadcast_containertype(AbstractArray) yields Array rather than Any. That incorrect return causes, e.g.,

julia> broadcast(==, [1], AbstractArray)
ERROR: MethodError: no method matching size(::Type{AbstractArray})
Closest candidates are:
  size{N}(::Any, ::Integer, ::Integer, ::Integer...) at abstractarray.jl:23
  size(::BitArray{1}) at bitarray.jl:49
  size(::BitArray{1}, ::Any) at bitarray.jl:53
  ...
Stacktrace:
 [1] broadcast_indices(::Type{Array}, ::Type{T}) at ./broadcast.jl:54
 [2] broadcast_c at ./broadcast.jl:290 [inlined]
 [3] broadcast(::Function, ::Array{Int64,1}, ::Type{T}) at ./broadcast.jl:406

This pull request addresses the above issue. Thanks to @ararslan for catching this issue in JuliaStats/DataArrays.jl#229!

[TotalVerb]

For clarity, this should perhaps be reordered so that all containertype methods are together, after all the _containertype methods.

It seems to me that the containertype(::Type) = Any method is redundant and can be removed, because _containertype(DataType) will already return Any.

[Sacha0]

Good call (and incorporated) on both counts. Thanks!

[TotalVerb]

We will need to inform packages about this change. I found these two uses:

• https://github.com/JuliaImages/ImageFiltering.jl/blob/df218608df9f61919b56562906a6628820721070/src/kernelfactors.jl
• https://github.com/JuliaParallel/DistributedArrays.jl/blob/a233591eecfddaf0e3441c46386159be497a053b/src/mapreduce.jl

[andreasnoack]

For ImageFiltering.jl, I think we can ping @timholy. I'll take care of DistributedArrays.jl.

[timholy]

I'll handle ImageFiltering.

[Sacha0]

Thanks all!