shell: Password prompt eats control characters

[Dan Jacobson]

M-x shell
$ ssh bla.bla.bla #or just:
$ echo -n Password:\ ; read
whereupon we are cleverly prompted for the password in the minibuffer.

Well, the password Bob sent me was in a different buffer, which one
needs to use C-x b to get to.

But no, every darn character, including C-x, is munched as part of the
password, Nazi style.

Until we hit ^G, which gives
  Warning: text will be echoed
which would have been fine with me, except that it is covered up by
  Quit
before we can see it.

So besides allowing e.g., C-x b to act normally, mention along with
the prompt some keys to escape...