demo(carousel): fixes broken image

Fixes broken image on first slide in the carousel demo 
Normalizes slide count display (Slide 1, 2, 3...)

Plunker: http://plnkr.co/edit/O4qDxoeXMs2urxsaJXTy?p=preview
Fixes issue: https://github.com/angular-ui/bootstrap/issues/2673


How about 601 + slides.length? 
And could you add a comment here stating that this is to get around the broken image on placekitten?