added #isAsync convenience method
added #isAsync convenience method

I'm not 100% sure this is a good idea; it made sense for a little
experimenting I wanted to do, and I figured it couldn't hurt to expose
it. I might remove it, though.

webcoding/lazy.js,DreamingPiggy/lazy.js,ddombrow/lazy.js,dtao/lazy.js,kwangkim/lazy.js,youprofit/lazy.js,Champii/lazy.js,dtao/lazy.js,VicNumber21/lazy.js,kwangkim/lazy.js,webcoding/lazy.js,oli5679/lazy.js,VicNumber21/lazy.js,Champii/lazy.js,DreamingPiggy/lazy.js,Champii/lazy.js,dtao/lazy.js,Deide/lazy.js,VicNumber21/lazy.js,webcoding/lazy.js,oli5679/lazy.js,gdseller/lazy.js,Deide/lazy.js,kwangkim/lazy.js,ddombrow/lazy.js,gdseller/lazy.js,oli5679/lazy.js,DreamingPiggy/lazy.js,youprofit/lazy.js,ddombrow/lazy.js,Deide/lazy.js,youprofit/lazy.js,gdseller/lazy.js