lufact should not require a square matrix

[gwhowell]

Here's the error code

function lufact{Tv<:UMFVTypes,Ti<:UMFITypes}(S::SparseMatrixCSC{Tv,Ti})
S.m == S.n || error("argument matrix must be square")

lu factorization of rectangular matrices is useful as a preconditioner for the normal
equation A'Ax = A'b (used for example by Wilkinson and Duff and Bjorck )

The option of using rectangular matrices is available in UMFPACK C code
and in the matlab and octave wrappers on it.