* extra check for images that return 3xx/4xx codes to be ignored
* API Key validation (error) message is returned to user
* error messages for images are displayed in the "ShortPixel Compression" column



git-svn-id: https://plugins.svn.wordpress.org/shortpixel-image-optimiser/trunk@1047877 b8457f37-d9ea-0310-8a92-e5e31aec5664