Description:
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ReflectionFunction for imagepng is missing last two parameters available since PHP 5.1.2 and 5.1.3 respectively, quality and filters.

PHP Version 7.1.1
GD library Version 2.2.3

Test script:
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$ref = new ReflectionFunction('imagepng'); 
var_dump(count($ref->getParameters()));

Expected result:
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int(4)

Actual result:
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int(2)