M6Web/picturefill-background — pull request #3 by robinnorth (2014-10-24 16:29:05+00:00)
Title: Only update matched background images if necessary on each run

Taking inspiration from Picturefill, I changed the behaviour of `picturefillBackground` to only update the background image of an element if necessary (i.e. if the current background image source differs from the matched source).