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/babeld/resend.h b/babeld/resend.h
new file mode 100644
index 0000000..fdb5730
--- /dev/null
+++ b/babeld/resend.h
@@ -0,0 +1,77 @@
+/*  
+ *  This file is free software: you may copy, redistribute and/or modify it  
+ *  under the terms of the GNU General Public License as published by the  
+ *  Free Software Foundation, either version 2 of the License, or (at your  
+ *  option) any later version.  
+ *  
+ *  This file is distributed in the hope that it will be useful, but  
+ *  WITHOUT ANY WARRANTY; without even the implied warranty of  
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU  
+ *  General Public License for more details.  
+ *  
+ *  You should have received a copy of the GNU General Public License  
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.  
+ *  
+ * This file incorporates work covered by the following copyright and  
+ * permission notice:  
+ *  
+Copyright (c) 2007, 2008 by Juliusz Chroboczek
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+*/
+
+#define REQUEST_TIMEOUT 65000
+#define UPDATE_MAX 4
+
+#define RESEND_REQUEST 1
+#define RESEND_UPDATE 2
+
+struct resend {
+    unsigned char kind;
+    unsigned char max;
+    unsigned short delay;
+    struct timeval time;
+    unsigned char prefix[16];
+    unsigned char plen;
+    unsigned short seqno;
+    unsigned char id[8];
+    struct interface *ifp;
+    struct resend *next;
+};
+
+extern struct timeval resend_time;
+
+struct resend *find_request(const unsigned char *prefix, unsigned char plen,
+                            struct resend **previous_return);
+void flush_resends(struct neighbour *neigh);
+int record_resend(int kind, const unsigned char *prefix, unsigned char plen,
+                   unsigned short seqno, const unsigned char *id,
+                   struct interface *ifp, int delay);
+int unsatisfied_request(const unsigned char *prefix, unsigned char plen,
+                        unsigned short seqno, const unsigned char *id);
+int request_redundant(struct interface *ifp,
+                      const unsigned char *prefix, unsigned char plen,
+                      unsigned short seqno, const unsigned char *id);
+int satisfy_request(const unsigned char *prefix, unsigned char plen,
+                    unsigned short seqno, const unsigned char *id,
+                    struct interface *ifp);
+
+void expire_resend(void);
+void recompute_resend_time(void);
+void do_resend(void);