Fix \ for AbstractVector LHS

Let \(::AbstractVector, ::AbstractMatrix) return a RowVector and
\(::AbstractVector, ::AbstractVector) return a scalar.

base/linalg/generic.jl

@@ -855,7 +855,7 @@ function (\)(A::AbstractMatrix, B::AbstractVecOrMat)
     return qrfact(A,Val(true)) \ B
 end
 
-(\)(a::AbstractVector, b::AbstractArray) = reshape(a, length(a), 1) \ b
+(\)(a::AbstractVector, b::AbstractArray) = pinv(a) * b
 (/)(A::AbstractVecOrMat, B::AbstractVecOrMat) = (B' \ A')'
 # \(A::StridedMatrix,x::Number) = inv(A)*x Should be added at some point when the old elementwise version has been deprecated long enough
 # /(x::Number,A::StridedMatrix) = x*inv(A)

test/linalg/dense.jl

@@ -76,7 +76,7 @@ bimg  = randn(n,2)/2
                 @test_throws DimensionMismatch b'\b
                 @test_throws DimensionMismatch b\b'
                 @test norm(a*x - b, 1)/norm(b) < ε*κ*n*2 # Ad hoc, revisit!
-                @test zeros(eltya,n)\ones(eltya,n) ≈ zeros(eltya,n,1)\ones(eltya,n,1)
+                @test zeros(eltya,n)\ones(eltya,n) ≈ (zeros(eltya,n,1)\ones(eltya,n,1))[1,1]
             end
 
             @testset "Test nullspace" begin