add allow_use_meta_url flag for settings.

Signed-off-by: Jack <jack.wgm@gmail.com>
fixed when define AVHTTP_DISABLE_THREAD, compile error.

Signed-off-by: Jack <jack.wgm@gmail.com>
I do not know why I want to do before, but doing so will lead to mistakes can not quit. fix it now!

Signed-off-by: Jack <jack.wgm@gmail.com>