nouveau: new bufferobj code.

nouveau: new bufferobj code.

The old code suffered from a number of issues, the most severe being that
with the Mesa VBO merge even swtcl used the driver's bufferobj interface.
On most VBO types (or non-AGP cards) the buffer ended up in vram, and
killed swtcl performance greatly.  All bufferobj's start in system memory
now, until they get referenced as a "real" VBO.

The other big change is that only potentially "damaged" areas are
uploaded/downloaded to/from the hardware.