Added Shader:getExternVariable(name).

Returns the base type name ('float', 'image', etc.), the number of components (2 for a vec2), and number of array elements (1 for a non-array variable) for the extern variable with the specified name in the shader.

Returns nil if the variable either doesn't exist or was optimized out by the driver's shader compiler.

src/modules/graphics/opengl/wrap_Shader.h

@@ -38,6 +38,7 @@ int w_Shader_sendFloat(lua_State *L);
 int w_Shader_sendMatrix(lua_State *L);
 int w_Shader_sendTexture(lua_State *L);
 int w_Shader_send(lua_State *L);
+int w_Shader_getExternVariable(lua_State *L);
 extern "C" int luaopen_shader(lua_State *L);
 
 } // opengl