Checks in playground's drawSprite. Playground frame more reliable.
Checks in playground's drawSprite. Playground frame more reliable.

Two things in this commit:

1. Fiesta.Playground's drawSprite now throws an error if the sprite is
   not a sprite

2. Fiesta.Playground's frame() does not halt if one object has a
   problem. The error is thrown into the console.

EvanHahn/Fiesta.js