Use the path to the running emacs

With this change, esup no longer requires emacs to be in the user's
$PATH. It picks up the path to emacs from the copy of emacs that it is
run from. This also guarantees that it will run with the same version
of emacs that it is run from, thus giving relevant results.

I have removed the reference to PATH from the readme.
Properly determine path to esup.el
Ensure emacs subprocess exits on error
Require cl in esup-batch
Merge pull request #2 from DarwinAwardWinner/master

Use the path to the running emacs