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