Revert all babel-related commits.

This reverts commit 27f689793a25a66cf62561ac1d1302e01983a805.
babeld initial import, for Babel routing protocol.

Conflicts:
	configure.ac
babeld: clean kernel_zebra (old functions, fields...).
babeld: address FreeBSD "struct route" issue

FreeBSD system headers have their own "struct route", which made it
impossible to compile babeld. Switching babeld to "struct babel_route".
babeld: address some compilation warnings

Including system headers is not necessary with zebra.h included and
sometimes results in "__ASSERT_FUNCTION redefined" compilation warning.

* babeld.c
  * babel_distribute_update_interface(): make static
* babel_interface.c
  * interface_config_write(): unused 'babel_ifp'
  * don't include system headers
* message.c
  * send_request(): unused 'babel_ifp'
  * send_multihop_request(): idem
  * don't include system headers
* route.c: don't include system headers
* xroute.c: idem
* source.h: newline at EOF
* message.h: idem
babeld: address some other compilation warnings.
babeld: fix bug concerning pidfile.
babeld: address remaining -Wcast-qual warnings

* net.c
  * babel_send(): arguments are not treated as "const", justify
    declaration
* babel_main.c: declare constant pointers as such
lib: update proto_redistnum() for Babel
babeld: bring babel_usage() into focus
babeld: add handling of "-z" cmdline arg
babeld: implement "show babel interface" command

* babel_interface.c
  * show_babel_interface_sub(): new function to process one ifp
  * show_babel_interface(): new function, VTY wrapper
  * babel_if_init(): update respectively
babeld: change fprintf(stderr) in term of zlog_err.
babeld: avoid segfault (bug 706).
babeld: add command: "show_babel_neighbour".
babeld: add command: "show_babel_database".
babeld: add command: "show_babel_running_config".
babeld: use zlog_debug instead of do_debugf, for debugf.
babeld: place the babel-state file in the quagga vars directory.
babeld: fix commands informations messages.