Added support for tinting rendermeshes
Added support for tinting rendermeshes

Rendermeshes have had a tint property for a while, but it
hasn't been honored.  Now the renderer will respect it
and apply the tint to the mesh upon rendering.  The tint
is a vec4, representing rgba, and is applied multiplicitively.

Change-Id: Ia08ceb63ee65a20d706004744990e1e067bf9af7

google/zooshi,google/zooshi,google/zooshi,google/zooshi,google/zooshi