fixed compiler warnings reported by gcc/clang

* changed some catch blocks to use exception references instead of value types
 * fixed missing use of SCR_WIDTH/SCR_HEIGHT for glfwCreateWindow
 * fixed implicit numeric type casts regarding signedness
 * removed unused variables

Signed-off-by: Toni Uhlig <matzeton@googlemail.com>

src/2.lighting/4.1.lighting_maps_diffuse_map/lighting_maps_diffuse.cpp

@@ -338,4 +338,4 @@ unsigned int loadTexture(char const * path)
     }
 
     return textureID;
-}
+}