add nd_geolocation_dbxref table

[nmenda]

create table nd_geolocation_dbxref ( nd_geolocation_dbxref_id bigserial not null, nd_geolocation_id bigint not null, dbxref_id bigint not null, is_current boolean not null default 'true', primary key (nd_geolocation_dbxref_id), foreign key (dbxref_id) references dbxref (dbxref_id) on delete cascade INITIALLY DEFERRED, foreign key (nd_geolocation_id) references nd_geolocation (nd_geolocation_id) on delete cascade INITIALLY DEFERRED, constraint nd_geolocation_dbxref_c1 unique (nd_geolocation_id,dbxref_id) ); create index nd_geolocation_dbxref_idx1 on nd_geolocation_dbxref (nd_geolocation_id); create index nd_geolocation_dbxref_idx2 on nd_geolocation_dbxref (dbxref_id);