Blender Git Loki

Cycles: Speedup by avoiding extra calculations in noise texture when unneeded

Noise texture is now faster when the color socket is unused. Potential for
speedup spotted by @nutel.

Some performance results:

Render Time Before After Difference
Gooseberry benchmark 47:51.34 45:55.57 -4%
Koro 12:24.92 12:18.46 -0.8%
Simple cube (Color socket) 48.53 48.72 +0.3%
Simple cube (Fac socket) 48.74 32.78 -32.7%
Goethe displacement 1:21.18 1:08.47 -15.6%
Cycles brick displacement 3:02.38 2:16.76 -25.0%
Large displacement scene 23:54.12 20:09.62 -15.6%

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D2513