Minor feature and compatibility improvements.

[silasp]

Hi there,

I used your code on a recent project and made some slight modifications: [1] Automatically resizes the placeholder image (if possible) [2] Updates Gd2.php to prevent issues if the php memory limit has been configured in Gb.

[obukhow]

Hi! Thank you for contributing! Unfortunately I cannot accept your pull-request because of license issues. You should not contribute any code with Magento copyrights, so you should exclude Varien_Image_Adapter_Gd2 class from pull-request.