Adding columns to primary key now adds not null constraint

[jycor]

Also added a test case to ensure adding not null constraint to primary key column does nothing.

[zachmu]

You need tests on CreateTable as well, same rules apply

[zachmu]

This looks good, but it needs tests for CREATE TABLE as well. Need to assert that primary key columns get a not null constraint on them (that remains there after the primary key is dropped).

This should fail, but passes in dolt today:

create table mpks (a int null, b int, primary key (a,b));

Try it in mysql and confirm. We should have bats tests for this.

[zachmu]

LGTM