Description:
------------
Running PostGreSQL 8.4, given a simple table like:

When using a bound parameter in prepare (named or unnamed) to a timestamp field, the parameter is improperly quoted resulting in errors on INSERT or UPDATE statements that are using expressions rather than simple datetime strings.

Reproduce code:
---------------
// In the postgresql database
CREATE TABLE foo
(
  id SERIAL UNIQUE NOT NULL,
  dtSometime TIMESTAMP WITH TIME ZONE NOT NULL
);

// Assuming $dbh is a connection to the above database
if ($stmt = $dbh->prepare('INSERT INTO foo (dtSometime) VALUES (:dtsometime)')
{
  if ($stmt->execute(array('now() + interval \'1 year\''))
  {
    print("ok!\n");
  }
  else
  {
    print_r($dbh->errorInfo());
  }
}

Expected result:
----------------
Expect a row to be inserted and 'ok!' to print.

Actual result:
--------------
The following is printed on the console:
//--cut
(   
    [0] => 00000
    [1] => 7
    [2] => ERROR:  invalid input syntax for type timestamp with time zone: "now() + interval '1 year'"
)
//--cut

A direct insert with the given SQL works fine as expected, so this must be a quoting issue that is forcing postgresql to interpret the expression as a literal datetime.