[Mesa-dev] Pipe control patches redux

[Kenneth Graunke]

Here's v3 of Daniel's PIPE_CONTROL series.  I reworked it substantially,
moving the length change to the beginning and splitting up the patches
into smaller ones that only do one thing at a time, to make it easier to
bisect or revert if there are any issues.  (I'm pretty paranoid when it
comes to PIPE_CONTROLs.)

If there are no objections, I'll push these tomorrow.