Description:
------------
imageline() now draws all horizontal and vertical lines as one pixel thick, whichever line thickness has been set using imagesetthickness(). As it worked fine before I upgraded to 5.2.1, this is probably caused by the recent optimisation of imageline().

Reproduce code:
---------------
<?php
$image=imagecreatetruecolor(400, 400);
$white = imagecolorallocate($image, 255, 255, 255);
$black = imagecolorallocate($image, 0, 0, 0);
imagefill($image, 0, 0, $white);
imagesetthickness($image, 10);

imageline($image, 200, 0, 200, 400, $black);
imageline($image, 0, 200, 400, 200, $black);
imageline($image, 0, 0, 392, 392, $black);

header("Content-type: image/gif");
imagegif($image);

imagedestroy($image);
?>

Expected result:
----------------
This should draw three lines, all 10 pixels thick.

Actual result:
--------------
Only the diagonal line is the correct thickness.