BUG: coint ignores autolag

[josef-pkt]

This was supposed to be fixed by #3966 which was closed without merging the fix.

currently autolag is hard coded to None in the coint call to adfuller and the keyword is ignored

[josef-pkt]

I'm not sure how to unit test this, the only information that we get is a different test statistic, and no information about which number of lags are used.
We can still assume that autolag in adfuller is correct. (i.e. no functional testing)

[josef-pkt]

Note, the critical values depend on nobs and not on the number of lags used.
So, the critical values do not depend on autolag.