TST: fixed test for gufuncs_linalg Det
ENH: cholesky handling of _potrf failures (set result to nan)
ENH: eigh, eigvalsh set result to nan on LAPACK error (_ssyevd, _heevd)
ENH: solve sets result to nan on LAPACK error (_gesv)
ENH: inv sets result to nan on LAPACK error (_gesv)
ENH: svd sets results to nan on LAPACK error (_gesdd)
ENH: chosolve sets result to nan on LAPACK error (_potrf, _potrs)
DOC: Added docstring for eigh