Fix T40078: GLSL Lamp with OnlyShadow makes weird colors in object.

To prevent only shadow lamps from producing negative colors, shr->diff
and shr->spec should've been clamped to positive values after lamp loop.
Fix T40438: Name of texture is not synchronize
Cleanup: Remove unused total power Emission code in Cycles, that was never exposed in the UI.

Differential Revision: https://developer.blender.org/D562