Blender Git Loki

Border rendering now works for all scenes used in compositor,
before this only active scene would be rendered with border.

When do_render_fields_blur_3d() is finished, it'll modify
render's display rect so it'll correspond bordered render
result placed on black backgrund. Actual border is stored
nowhere, which makes it only way to re-calculate disprect
for all other renders used in compo based on source. Not
so big deal actually.

Also needed to modify Cycles a bit, because before this
patch it used border settings from scene being rendered.
Now made it so render data is passing to external engines.

Using a property inside RenderEngine structure for this.
Not best ever design for passing render data, but this
would prevent API breakage. So now external engines could
access engine.render to access active rendering settings.

Reviewed by Brecht, thanks!