Freestyle: debug statistics on stroke rendering.
Freestyle: time/space optimization in stroke rendering without textures.

When strokes do not have textures assigned, UV coordinates are not computed now.
This will save a bit of time and space in stroke rendering.
Freestyle: minor code clean-up.
Cycles: add support for "Use Alpha" option on image datablocks.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D486
Nodes: add absolute value operation to all math nodes

Reviewed By: dingto, brecht

Differential Revision: https://developer.blender.org/D507
Cycles-Bake: Subsurface Scattering support (fix T40060)

This fixes the SSS Direct/Indirect passes as well as the Combined pass.
Patch reviewed and with fixes and contributions from Brecht van Lommel.

Note: displacement/bump map (related to the report) will be handled separately

Reviewers: brecht

Differential Revision: https://developer.blender.org/D503