Applied patch [#34178] tile rendering for fast gaussian blur

Thanks to David M (erwin94)
only added some comments.

https://projects.blender.org/tracker/?func=detail&aid=34178&group_id=9&atid=127
 


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk@60863 954f8c5b-7b00-dc11-b283-0030488c597c