* 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 appreciate what these two functions are trying to accomplish, but they
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.