Partial code review for ALTER DOMAIN patch. Incorporates Rod Taylor's

patches of 9-Dec (permissions fix) and 13-Dec (performance) as well as
a partial fix for locking issues: concurrent DROP COLUMN should not
create trouble anymore.  But concurrent DROP TABLE is still a risk, and
there is no protection at all against creating a column of a domain while
we are altering the domain.

src/test/regress/expected/domain.out

@@ -201,19 +201,19 @@ create table domnotnull
 );
 insert into domnotnull default values;
 alter domain dnotnulltest set not null; -- fails
-ERROR:  ALTER DOMAIN: Relation "domnotnull" Attribute "col1" contains NULL values
+ERROR:  ALTER DOMAIN: Relation "domnotnull" attribute "col1" contains NULL values
 update domnotnull set col1 = 5;
 alter domain dnotnulltest set not null; -- fails
-ERROR:  ALTER DOMAIN: Relation "domnotnull" Attribute "col2" contains NULL values
+ERROR:  ALTER DOMAIN: Relation "domnotnull" attribute "col2" contains NULL values
 update domnotnull set col2 = 6;
 alter domain dnotnulltest set not null;
 alter domain dnotnulltest set not null; -- fails
-ERROR:  AlterDomain: dnotnulltest is already set to NOT NULL
+NOTICE:  AlterDomain: dnotnulltest is already set to NOT NULL
 update domnotnull set col1 = null; -- fails
 ERROR:  Domain dnotnulltest does not allow NULL values
 alter domain dnotnulltest drop not null;
 alter domain dnotnulltest drop not null; -- fails
-ERROR:  AlterDomain: dnotnulltest is already set to NULL
+NOTICE:  AlterDomain: dnotnulltest is already set to NULL
 update domnotnull set col1 = null;
 drop domain dnotnulltest cascade;
 NOTICE:  Drop cascades to table domnotnull column col2
@@ -253,7 +253,7 @@ create table domcontest (col1 con);
 insert into domcontest values (1);
 insert into domcontest values (2);
 alter domain con add constraint t check (VALUE < 1); -- fails
-ERROR:  AlterDomainAddConstraint: Domain con constraint t failed
+ERROR:  ALTER DOMAIN: Relation "domcontest" attribute "col1" contains values that fail the new constraint
 alter domain con add constraint t check (VALUE < 34);
 alter domain con add check (VALUE > 0);
 insert into domcontest values (-5); -- fails