Recommend move eshell/su and eshell/sudo to em-tramp.el

[John Wiegley]

Something I've noticed after moving to Emacs 24 is that using "sudo" in Eshell
has become an awful experience:

    - It's *much* slower than *sudo (by orders of magnitude)
    - It doesn't show any output until the command is done
    - It locks up Emacs until the command is done

I find this behavior unfortunate, since sudo is such a common command for
users of Eshell to use.  It was added in 2009 by the Tramp author:

    2009-11-27  Michael Albinus  <address@hidden>

           * eshell/em-unix.el (eshell/su, eshell/sudo): New defuns,
           providing a Tramp related implementation of "su" and "sudo".
           (eshell-unix-initialize): Add "su" and "sudo".

I do not believe these should not have been made the default.  I recommend
moving them out of em-unix.el and into a new module, em-tramp.el, which is OFF
by default.  Users who prefer to use Tramp for everything can turn it on, and
a note to that effect should be added to the Tramp manual.

John