isone(A) throws error when A is not a StridedMatrix

[dlfivefifty]

This is inconsistent (I came across it while looking through Base to see if I can resolve #10385):

julia> V = view(rand(5,5), [1,3,4], :)
3×5 view(::Array{Float64,2}, [1, 3, 4], :) with eltype Float64:
 0.68645    0.906707  0.474079  0.156336  0.689158 
 0.0366613  0.705923  0.286435  0.169441  0.0788967
 0.602231   0.19818   0.883198  0.796978  0.416841 

julia> isone(V)
ERROR: DimensionMismatch("multiplicative identity defined only for square matrices")
Stacktrace:
 [1] _one at ./array.jl:393 [inlined]
 [2] one at ./array.jl:397 [inlined]
 [3] isone(::SubArray{Float64,2,Array{Float64,2},Tuple{Array{Int64,1},Base.Slice{Base.OneTo{Int64}}},false}) at ./number.jl:45
 [4] top-level scope

julia> isone(rand(3,5))
false

A simple fix is to replace isone(A::StridedMatrix) definition with isone(A::AbstractMatrix).

(I don't see any reason why the definitions for isone were specialized to StridedMatrix.)

[ThatcherT]

I'm a first time contributor so I'm not entirely sure I've done this correctly. I opened up a pull request with the changes suggested by @dlfivefifty and I added a simple test. Do I need to take anymore action @sostock?