Description:
------------
The following emerged after upgrading from 5.2.0 to 5.2.1 and has been checked in both versions: the error only occurs in 5.2.1 .

When passing parameters into a LIMIT clause using PDO::execute(), it appears that PDO is quoting the parameters, which causes MYSQL to throw an error. 

FYI: PDO_MYSQL is built against MySQL client library 5.0.18.

Reproduce code:
---------------
$dbh = new PDO('mysql:localhost;dbname=my_db', 'user', '' );
$dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

try{

	$query = $dbh->prepare( 'SELECT * FROM some_table LIMIT :start, :limit' );
	
	if 	( $query->execute ( array ( 'start' => 0, 'limit' => 10 ) ) )
	{
		while ( $row = $query->fetch ( PDO::FETCH_ASSOC ) )
		{
			print_r($row);
		}
		$query->closeCursor();
	}

} catch( Exception $e ){
	print_r( $e );
}


Expected result:
----------------
A number of rows are returned.

Actual result:
--------------
An exception is thrown:

PDOException Object
(
    [message:protected] => SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''0', '10'' at line 1
    [string:private] => 
    [code:protected] => 42000
    [file:protected] => [my_file].php
    [line:protected] => 19
    [trace:private] => Array
        (
            [0] => Array
                (
                    [file] => [my_file].php
                    [line] => 19
                    [function] => execute
                    [class] => PDOStatement
                    [type] => ->
                    [args] => Array
                        (
                            [0] => Array
                                (
                                    [start] => 0
                                    [limit] => 10
                                )

                        )

                )

        )

    [errorInfo] => Array
        (
            [0] => 42000
            [1] => 1064
            [2] => You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''0', '10'' at line 1
        )

)