Description:
------------
PDO::ATTR_EMULATE_PREPARES changes behavior of parameter processing.
When it is enabled multiple occurrences of named parameter work as expected, but 
when it is disabled I get "Invalid parameter number" error.

Test script:
---------------
<?php
  $pdo = new PDO('mysql:host=localhost;dbname=test', 'root', '');
  $pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, false); /// remove this line and scirpt works as expected
  $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
  $query = $pdo->prepare('select :x = :x');
  $query->bindValue(':x', 1);
  $query->execute();
  $t = $query->fetch();
  var_dump($t);
  $query->closeCursor();

Expected result:
----------------
array(2) {
  '\'1\' = \'1\'' =>
  string(1) "1"
  [0] =>
  string(1) "1"
}

Actual result:
--------------
PDOException: SQLSTATE[HY093]: Invalid parameter number in 
/srv/http/fucktube/app/test.php on line 7

Call Stack:
    0.0002     230552   1. {main}() /srv/http/fucktube/app/test.php:0
    0.0739     246416   2. PDOStatement->execute() 
/srv/http/fucktube/app/test.php:7