onload redirection

[Katsumi Yamaoka <yamaoka@xxxxxxx>]

Hi,

I've added the `onload redirection' feature.  When logging in to
certain sites, it will bring you to an `OpenID transaction' page,
not a page you want to go directly.  You have to push a submit
button there, and moreover it will not necessarily be only once.
But this feature does those troublesome operations automatically.
Tested it with https://mainichi.jp/ (I have a login account).

Unfortunately, I was unable to make the `w3m-retrieve' function
work asynchronously for those redirections in one funcall.  If
only it could do, `w3m-retrieve' could get more handy.  So, now
the onload redirections work synchronously, and this is also why
I made a change in also shimbun.el.

OTOH, I found that some sites, e.g., Amazon, are unable to be
logged in regardless of this change.  I'd like to fix it when I
have time.

Regards,

P.S. I will be absent for about a week from tomorrow.