Comment 0 for bug 440151

the tests for dimension of exog, endog for model fail because -if is not equal -inf.
The source I think is if exog is only 1d or one column, then the df_model = 0, which, I think, causes a zero division for fvalue and mse_model

It is necessary to fix test and to check whether the -inf result is actually correct.
I did the initial correction in the test for fvalue, but commented it out again, because we need to check first if -inf is correct.