Description:
------------
I cannot use printer_set_option() to specify the orientation of the paper.

Reproduce code:
---------------
---
From manual page: function.printer-set-option#Parameters
---
<?php 
$ptr=printer_open("HP LaserJet 6P");
printer_start_doc($ptr);
printer_set_option($ptr,PRINTER_ORIENTATION,PRINTER_ORIENTATION_LANDSCAPE);
printer_start_page($ptr);
printer_write($ptr,"The letter is sidelong.");
printer_close($ptr); 
?>

Expected result:
----------------
I can specify the orientation of the paper to be sidelong.

Actual result:
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It doesn't change.