Update picturefill.js
Update picturefill.js

Set title-attribute (missing in the proposal yet)
footiealf/picturefill,rockmandew/picturefill,patrickkettner/picturefill,mcanthony/picturefill,patrickkettner/picturefill,purposeindustries/picturefill,rockmandew/picturefill,yubin-huang/picturefill,jansepar/picturefill,samiadelgado/picturefill,yufi113/picturefill,albell/picturefill,scottjehl/picturefill,chrismcandrew/picturefill,mcanthony/picturefill,yufi113/picturefill,guardian/picturefill,guardian/picturefill,chrismcandrew/picturefill,iancrowther/picturefill,yubin-huang/picturefill,ddeveloperr/picturefill,nucliweb/picturefill,purposeindustries/picturefill,samiadelgado/picturefill,demateu/picturefill,ddeveloperr/picturefill,demateu/picturefill,albell/picturefill,scottjehl/picturefill,iancrowther/picturefill,footiealf/picturefill