Made windows test show all windows at once.

tests/windows.c

@@ -91,9 +91,11 @@ int main(void)
         glfwSetWindowPos(windows[i],
                          100 + (i & 1) * (200 + left + right),
                          100 + (i >> 1) * (200 + top + bottom));
-        glfwShowWindow(windows[i]);
     }
 
+    for (i = 0;  i < 4;  i++)
+        glfwShowWindow(windows[i]);
+
     while (running)
     {
         for (i = 0;  i < 4;  i++)