Panic when altering the PK on a table with column defaults

[fulghum]

The following statements trigger a panic in Dolt because Type() is called on UnresolvedColumnDefault.

create table t (id varchar(128), c1 int not null default '-1', c2 timestamp not null default CURRENT_TIMESTAMP, c3 int not null default (id));
alter table t add primary key `prikey`(id);