glsl framebuffer_fetch extension check at runtime

src/shader.h

@@ -84,6 +84,7 @@ class ShaderManager
     static std::map<kShader, Shader> m_shaders;
     static Shader* m_current;
 public:
+    static bool ext_framebuffer_fetch;
     static bool create(kShader id, const char* vertex, const char* fragment);
     static void use(kShader id);
     static void use(const char* name);