Description:
------------
getimagesize does not contain 'channel' in the returning array when you run 
getimagesize on a PNG or BMP image.

The documentation (http://php.net/manual/en/function.getimagesize.php) specifies 
that it will always return an array with 7 elements. This does not seem to be the 
case. Se script output below.

Test script:
---------------
<?php
$file_jpg = "test.jpg";
$file_png = "tux.png";

$info_jpg = getimagesize($file_jpg);
$info_png = getimagesize($file_png);

echo "\nJPG:";
print_r($info_jpg);

echo "\nPNG:";
print_r($info_png);
?>


Expected result:
----------------
JPG:Array
(
    [0] => 463
    [1] => 399
    [2] => 2
    [3] => width="463" height="399"
    [bits] => 8
    [channels] => 3
    [mime] => image/jpeg
)

PNG:Array
(
    [0] => 400
    [1] => 479
    [2] => 3
    [3] => width="400" height="479"
    [bits] => 8
    [channels] => 4
    [mime] => image/png
)


Actual result:
--------------
JPG:Array
(
    [0] => 463
    [1] => 399
    [2] => 2
    [3] => width="463" height="399"
    [bits] => 8
    [channels] => 3
    [mime] => image/jpeg
)

PNG:Array
(
    [0] => 400
    [1] => 479
    [2] => 3
    [3] => width="400" height="479"
    [bits] => 8
    [mime] => image/png
)