File Release Notes and Changelog

Build fixes, ocaml 4 compatibility.

* src/discover.ml :
  * New option -q to suppress stderr
  * --disable-* options to exclude selected features from build
* More precise test for `sendmsg` (bug #1162)
* Fix FTBFS on kfreebsd-* (Debian patch)
* Unit tests are disabled by default and oUnit is now an optional dependency,
  configure with --enable-tests to build tests
* OCaml 4 compatibility (Unix.open_flag)
* List email contacts (bug #1108)