Description:
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pg_convert() does not accept an ISO 8601 date/time string, but will if the character "T" is replaced with whitespace. This is inconsistent with the constant DateTime::ISO8601 and date("c").

I believe if the regex in pgsql.c for case PG_TIMESTAMP (line 6165) can be improved (see patch).

Test script:
---------------
$db = pg_connect("dbname=test user=test");

pg_query($db, "CREATE TABLE public.test_table ( test_field TIMESTAMPTZ )");

// ISO 8601 (with 'T' between date and time)
$date_string_php_iso8601 = date_create('8 Dec 2015 5:38')->format(DateTime::ISO8601);

// ISO 8601 with the 'T' removed
$modified_format = 'Y-m-d H:i:sO';
$date_string_modified_iso8601 = date_create('8 Dec 2015 5:38')->format($modified_format);

printf("trying format %s \n", DateTime::ISO8601);
pg_convert($db, 'public.test_table', ['test_field' => $date_string_php_iso8601]);

printf("trying format %s \n", $modified_format);
pg_convert($db, 'public.test_table', ['test_field' => $date_string_modified_iso8601]);

print "done\n";

pg_query($db, "DROP TABLE test_table");


Expected result:
----------------
trying format Y-m-d\TH:i:sO 
trying format Y-m-d H:i:sO 
done


Actual result:
--------------
trying format Y-m-d\TH:i:sO 
PHP Notice:  pg_convert(): Expects NULL or string for PostgreSQL timestamptz field (test_field) in /Users/dlt/Desktop/bug.php on line 16

Notice: pg_convert(): Expects NULL or string for PostgreSQL timestamptz field (test_field) in /Users/dlt/Desktop/bug.php on line 16
trying format Y-m-d H:i:sO 
done