Chow predictive failure test
[fstat,f_pvalue,dfnum,dfden]=predfailin0(res,n1,np)
resulols = a results tlist from a first stage estimation
n1 = # of observations of the sub-period
fstat = value of the test statistic
f_pvalue = its p-value
dfnum = # dof of the numerator
dfden = # dof of the denominator