Description:
------------
The pg_insert and pg_update functions will not accept now() as a valid value for timestamp fields.

Reproduce code:
---------------
// Assumes the following table exists:
/*
  CREATE TABLE timestamp_test
  (
    id serial NOT NULL, 
    mytime timestamp NOT NULL,
    CONSTRAINT timestamp_test_pkey PRIMARY KEY (id)
   )
   WITHOUT OIDS;
*/


$dbConn = pg_connect();

$values = array('mytime' => 'now()');
pg_insert($dbConn, 'timestamp_test', $values);

$ids = array('id' => 1);
$fields = array('mytime' => 'now()');
pg_update($dbConn, 'timestamp_test', $fields, $ids);

Expected result:
----------------
Both the insert and the update should succeed.

Actual result:
--------------
Error Log:

PHP Notice:  pg_insert() [<a href='function.pg-insert'>function.pg-insert</a>]: 'now()' does not match with '^([0-9]{4}[/-][0-9]{1,2}[/-][0-9]{1,2})([ \t]+(([0-9]{1,2}:[0-9]{1,2}){1}(:[0-9]{1,2}){0,1}(\.[0-9]+){0,1}([ \t]*([+-][0-9]{1,2}(:[0-9]{1,2}){0,1}|[a-zA-Z]{1,5})){0,1})){0,1}$' 

PHP Notice:  pg_insert() [<a href='function.pg-insert'>function.pg-insert</a>]: Expects NULL or string for PostgreSQL timestamp field (mytime)

PHP Notice:  pg_update() [<a href='function.pg-update'>function.pg-update</a>]: 'now()' does not match with '^([0-9]{4}[/-][0-9]{1,2}[/-][0-9]{1,2})([ \t]+(([0-9]{1,2}:[0-9]{1,2}){1}(:[0-9]{1,2}){0,1}(\.[0-9]+){0,1}([ \t]*([+-][0-9]{1,2}(:[0-9]{1,2}){0,1}|[a-zA-Z]{1,5})){0,1})){0,1}$' 

PHP Notice:  pg_update() [<a href='function.pg-update'>function.pg-update</a>]: Expects NULL or string for PostgreSQL timestamp field (mytime)