#22 Add support to distribute on other than unique column

[Abbas Butt]

create table blood_gp(bg_id integer PRIMARY KEY, pos integer, bg_name varchar(20)) distribute by modulo (pos);
results in
ERROR: Unique index of partitioned table must contain the hash/modulo distribution column.

This needs some fundamental work to solve. We need to enforce the uniqueness (or other constraints) globally among all the nodes involved.

[Koichi Suzuki]

Global constraint issue.