Blender Git Loki

Cuda use streams and async to avoid busywaiting

This is my first stab at this and is based on this IRC converstation:

<mib2berlin> brecht: this is meaning as reminder only, I know you have other things to do > http://openvidia.sourceforge.net/index.php/Optimization_Notes#avoiding_busy_waits
<brecht> mib2berlin: thanks, bookmarked

only tested on Ubuntu 14.04 / cuda 5.0 but ill do some more testing tomorrow.

Also unsure about the placement and the lifetime of the stream and the event. But creating / deleting these seems to incur a non trivial cost.

Reviewers: brecht

Reviewed By: brecht

CC: mib2berlin, dingto

Differential Revision: https://developer.blender.org/D262