[Mesa-dev] Initial support for EXT_external_objects v4

[Timothy Arceri]

Hi all,

Andres is not around at the moment so as well are reviewing the
remaining patches I've rebased and added all Marek's suggestions.

I've also made a few minor changes (see commit messages) and
reworked some of the patches to reduce code churn.

I thought I'd send it out one last time to see if there was any
more feedback otherwise I'll probably push later in the week.

Thanks,
Tim 

Series available at:
  https://github.com/tarceri/Mesa.git (memobj2)