final patch - plpgsql: for-in-array

Hello

this patch implement a new iteration construct - iteration over an
array. The sense of this new iteration is:
  * a simple and cleaner syntax
  * a faster execution - this bring down a number of detoast operations

create or replace function subscripts(anyarray, int)
returns int[] as $$
select array(select generate_subscripts($1,$2));
$$ language sql;

create or replace function fora_test()
returns int as $$
declare x int; s int = 0;
   a int[] := array[1,2,3,4,5,6,7,8,9,10];
begin
  for x in array subscripts(a, 1)
  loop
    s := s + a[x];
  end loop;
  return s;
end;
$$ language plpgsql;

create or replace function fora_test()
returns int as $$
declare x int; s int = 0;
begin
  for x in array array[1,2,3,4,5,6,7,8,9,10]
  loop
    s := s + x;
  end loop;
  return s;
end;
$$ language plpgsql;

create or replace function fora_test()
returns int as $$
declare x int; y int;
   a fora_point[] := array[(1,2),(3,4),(5,6)];
begin
  for x, y in array a
  loop
    raise notice 'point=%,%', x, y;
  end loop;
  return 0;
end;
$$ language plpgsql;

Regards

Pavel Stehule