bug#3767: 23.0.94; Functions in password-cache should be autoloaded

[Chong Yidong <cyd@stupidchicken.com>]

> I was wondering why jabber.el didn't cache my password, even though I
> set password-cache and password-cache-expiry correctly, and found the
> reason: jabber.el checks whether the running Emacs is new enough to have
> password-cache.el by (fboundp 'password-read), but this function is not
> autoloaded.  The problem is masked if you use Gnus.
>
> Thus I propose that at least `password-read' be autoloaded, possibly
> others as well.

I think jabber.el should use the NOERROR argument to `require':

  (if (require 'password-cache nil t)
      use-password-cache
    do-alternative)