USING INDEX TABLESPACE

The attached patch allows the specification of the tablespace the index
is to be created in for unique and pk constraints. It also fixes the
dumping of such constraints so that they are restored into the correct
tablespace, after they have been moved with SET TABLESPACE. This is
currently an outstanding pg_dump bug.

The syntax is exactly what Oracle uses as far as i can tell, and I think
that we need 'using index' in there, because it's the index that's in a
tablespace, NOT the constraint itself.

Includes docs.

eg:

create table test (a integer primary key index tablespace loc);

create table test (a integer unique index tablespace loc);

create table test (a integer);
alter table test add primary key(a) index tablespace loc;

create table test (a integer);
alter table test add unique(a) index tablespace loc;

Chris