Also reimplemented screen clearing as a color quad to support alpha blending when clearing as in the original hardware.
the funny thing is how is implemented peeking, as locking depth textures is not supported, implemented peeking copying the values form the depth texture to a r32f render target and then reading back the data.
please a lot of testing to this commit.
git-svn-id: https://dolphin-emu.googlecode.com/svn/trunk@4599 8ced0084-cf51-0410-be5f-012b33b47a6e