sparse lufact fallback not correctly defined

[jiahao]

In trying to troubleshoot #301, I discovered that the following code seems to result in an infinite loop in SparseArrays.normestinv, an unexported function for estimating the norm of the inverse of the input sparse matrix.

julia> srand(5); Ac = sprandn(20,20,.5) + im* sprandn(20, 20,.5);

julia> Af = convert(SparseMatrixCSC{Complex64}, Ac);

julia> SparseArrays.normestinv(Af, 1) #hangs

Probably related:

julia> SparseArrays.normestinv(sparse(ones(Complex64, 1, 1)), 1)
ERROR: StackOverflowError:
 in float at operators.jl:381
 in call at essentials.jl:56 (repeats 509 times)

[jiahao]

The offending recursion appears to be in sparse/umfpack.jl:

typealias UMFVTypes Union{Float64,Complex128}
...
lufact{Tv<:UMFVTypes,Ti<:UMFITypes}(S::SparseMatrixCSC{Tv,Ti}) = ...
lufact(A::SparseMatrixCSC) = lufact(float(A))

Because Complex64 is not supported by UMFPACK, the fallback method gets called infinitely.