* Add full PMODE register to replace slbg/mmod
* Add full EXTBUF register (will allow to emulate write feedback)
* Add a third source (which will actually be the destination of the
write feedback)
Check the instruction set first in GPUinit, GPUconfigure and GPUtext
to prevent unsupported vector instructions from being executed.
Move the vector initialisation in GPUinit to a separate function - it
avoids a vzeroupper instruction.
vector push_back causes a SIGILL signal on a Nehalem (SSE4.2) QEMU VM
when compiled with GCC 6.1.1.
However, an empty constructor causes illegal instruction exceptions to be
generated on a Windows VM.
So here's an inbetween that looks stupid but works on what I've tested.
Jonathan Li