Direct3D9 support

[Henrik]

Those of you who can't use OpenGL 2.0 on your ancient PCs can now try the D3D9 backend, on the latest Windows builds:

* Open Memstick/PSP/SYSTEM/ppsspp.ini
* Under [Graphics], change the setting GPUBackend to 1.

On startup, PPSSPP should now show "Direct3D9" at the bottom instead of OpenGL.

The Direct3D backend is still very immature but some games are now quite playable, it's pretty similar to how the OpenGL backend worked a year ago.

It's not time to file issue reports yet but it would be interesting to hear how well it runs on various low end machines.


Later, we will also add a D3D11 backend which will allow porting to Windows Phone. However it's hard to say if we are going to get good enough performance without a JIT, as JITs are still not allowed on Windows Phone.