Updated Terrain test to use a 3 splat layers instead of 2.

Misc other tweaks to Terrain test.

gameplay/src/TerrainPatch.cpp

@@ -667,6 +667,10 @@ TerrainPatch::Layer::~Layer()
 {
 }
 
+TerrainPatch::Level::Level() : model(NULL)
+{
+}
+
 bool TerrainPatch::LayerCompare::operator() (const Layer* lhs, const Layer* rhs) const
 {
     return (lhs->index < rhs->index);

gameplay/src/TerrainPatch.h

@@ -41,6 +41,8 @@ private:
     struct Level
     {
         Model* model;
+
+        Level();
     };
 
     struct LayerCompare