[yt-dev] [yt_analysis/yt] Projections should switch off parallel reduction method (issue #549)

[Matthew Turk]

New issue 549: Projections should switch off parallel reduction method
https://bitbucket.org/yt_analysis/yt/issue/549/projections-should-switch-off-parallel

Matthew Turk:

For those simulation types where the global mesh is known, we should use the (slightly more scalable) global mesh information to pre-construct the quadtree which is then reduced as an array across all processors.  For those simulation types where we do not know the global mesh information, we should fall back on the quadtree reduction method we used before, which is in the routine `merge_quadtree_buffers` in `parallel_analysis_interface`.

This will require a flag or some type of discriminator between global/local mesh simulations.

Responsible: MatthewTurk