Added testing of glfwShowWindow and GLFW_VISIBLE.

tests/windows.c

@@ -55,6 +55,8 @@ int main(void)
 
     for (i = 0;  i < 4;  i++)
     {
+        glfwWindowHint(GLFW_VISIBLE, GL_FALSE);
+
         windows[i] = glfwCreateWindow(200, 200, GLFW_WINDOWED, titles[i], NULL);
         if (!windows[i])
         {
@@ -71,6 +73,7 @@ int main(void)
                      0.f);
 
         glfwSetWindowPos(windows[i], 100 + (i & 1) * 300, 100 + (i >> 1) * 300);
+        glfwShowWindow(windows[i]);
     }
 
     while (running)