In the ad for the movie, you see (the part where the thieves are singing and pointed knives at Aladdin) you see he has a blood stain on his arm, a little above his elbow, but in the movie, his arm is fine.
I just realized that...
In the movie he is cut, and we see the stain, but when they get to singing, it is gone-
yet in the previews, we still see the stain, and he is holding it.
the hole in his shirt is still there though.
I would just like to mention that in most, if not all, Disney movies there is no blood used. There may be death, but there is no blood. So, this isn't really a slip-up in my opinion. I think that someone just decided that it wasn't the right time to introduce blood in Disney movies, so they changed their mind after the trailer was released. Either that, or someone screwed up and drew the blood when they knew, but forgot, that blood is not used in Disney. However, in Tarzan, which I'm sure is Disney, there is blood on the floor when his parents are killed. This may be the first blood in Disney. Just thought I'd let you know!