babeld: Initial import, for Babel routing protocol.

* Initial import of the Babel routing protocol, ported to Quagga.
* LICENCE: Update the original LICENCE file to include all known potentially
  applicable copyright claims.  Ask that any future contributors to babeld/
  grant MIT/X11 licence to their work.
* *.{c,h}: Add GPL headers, in according with the SFLC guidance on
  dealing with potentially mixed GPL/other licensed work, at:

  https://www.softwarefreedom.org/resources/2007/gpl-non-gpl-collaboration.html
diff --git a/lib/zclient.h b/lib/zclient.h
index 73389ec..a7d7b54 100644
--- a/lib/zclient.h
+++ b/lib/zclient.h
@@ -22,6 +22,9 @@
 #ifndef _ZEBRA_ZCLIENT_H
 #define _ZEBRA_ZCLIENT_H
 
+/* For struct zapi_ipv{4,6}. */
+#include "prefix.h"
+
 /* For struct interface and struct connected. */
 #include "if.h"