add test for sprite blending

git-svn-id: https://svn.code.sf.net/p/desmume/code/trunk@4790 5577840e-afb3-4e59-9ef3-2b7f898b1952
fix some sprite blending cases, regression post 0.9.9. fixes bug #1338

git-svn-id: https://svn.code.sf.net/p/desmume/code/trunk@4791 5577840e-afb3-4e59-9ef3-2b7f898b1952
spriteblend test also tests whether window or bg priority logic applies first

git-svn-id: https://svn.code.sf.net/p/desmume/code/trunk@4792 5577840e-afb3-4e59-9ef3-2b7f898b1952