[Mesa3d-dev] context transfers again

[Keith W. <ke...@vm...>]

I've pushed a cleaned-up version of this branch to
gallium-context-transfers-2.  Despite its long history, this branch is a
fairly straightforward change, moving transfers to pipe_context.  

We've had to do quite a bit of work elsewhere to make this change
feasible, but having done that it's not too invasive.  I hope people can
take a look at it & I'll aim to merge in the next few days.

Keith