Added DoD Distribution Statement A, which pertains to DARPA's support for
certain portions of the Emulab software.  The statement says that these
portions of Emulab are "approved for public release; distribution is
unlimited."

Also performed other various cleanups: put two blank lines before headings;
indent displayed URLs and email addresses consistently; fixed a typo in the
emulab-users list URL; and fixed punctuation around quotes.