EMI: Sprite and shadow fixes

This fixes some issues observable for example in the sets shi and unc. See my [blog post](http://akzgsoc.blogspot.fi/2014/08/bug-squashing.html) for details and comparison screenshots.

Also, 45606bf fixes an issue in TinyGL. TinyGL previously ignored the TGL_DEPTH_TEST flag (depth testing was always done regardless of it). The depth test may be disabled when drawing sprites in EMI, so I added support for this.