Description:
------------
For "SELECT field1, field2 FROM table"
pg_field_name() returns "field1" and "field2", but for "SELECT 'field1', 'field2' FROM table" (when fields name in single quotes) returns "?column?" and "?column?".

PostgreSQL(libpq) Version  7.4.2

Reproduce code:
---------------
$pc = pg_connect("dbname=webmail");

$res = pg_query($pc, "SELECT 'userid', 'domainid' FROM users WHERE userid=1");
$num = pg_num_fields($res);
for ($i=0; $i<$num; $i++)
{
	$fieldname = pg_field_name($res, $i);
	echo "column $i: $fieldname <br>";
}


Expected result:
----------------
column 0: userid
column 1: domainid

Actual result:
--------------
column 0: ?column?
column 1: ?column?