Fix: PictureFill issue with older version of PHP.
Fix: issue with boolean values in the options.
Fix: PictureFill method now ignore fallback img tags found in picture tags.
Change: logging enhanced for PictureFill.

git-svn-id: https://plugins.svn.wordpress.org/wp-retina-2x/trunk@931504 b8457f37-d9ea-0310-8a92-e5e31aec5664