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/LICENCE b/babeld/LICENCE
new file mode 100644
index 0000000..9da569d
--- /dev/null
+++ b/babeld/LICENCE
@@ -0,0 +1,36 @@
+Code in this directory is made available under the following licence:
+
+  ---------------------------------------------------------------------------
+  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.
+  ---------------------------------------------------------------------------
+
+The code also makes calls to and links with the "libzebra" code of Quagga,
+in the lib/ directory of this project, which is subject to the GPL licence
+as given in the top-level COPYING file included with Quagga.
+
+Contributors to the code in babeld/ are asked to make their work available
+under the same MIT/X11 licence as given immediately above.  Please indicate
+your assent to this by updating this file and appending the appropriate
+
+  Copyright <year> <Author name>, <author contact details>
+
+line to the existing copyright assertion lines in the MIT/X11 licence text
+above in this file.