fix elements selection
fix elements selection

always include images if they have a ‘sizes’ attribute, even when
‘srcset’ is supported by browser

iancrowther/picturefill,albell/picturefill,footiealf/picturefill,yubin-huang/picturefill,samiadelgado/picturefill,chrismcandrew/picturefill,footiealf/picturefill,patrickkettner/picturefill,purposeindustries/picturefill,iancrowther/picturefill,guardian/picturefill,yufi113/picturefill,rockmandew/picturefill,demateu/picturefill,ddeveloperr/picturefill,ddeveloperr/picturefill,guardian/picturefill,yufi113/picturefill,scottjehl/picturefill,patrickkettner/picturefill,mcanthony/picturefill,demateu/picturefill,rockmandew/picturefill,nucliweb/picturefill,albell/picturefill,mcanthony/picturefill,chrismcandrew/picturefill,yubin-huang/picturefill,purposeindustries/picturefill,scottjehl/picturefill,samiadelgado/picturefill