Add OpenSSL licensing exception

debian/copyright

@@ -4,7 +4,7 @@ Source: http://github.com/keithw/mosh
 
 Files: *
 Copyright: 2012 Keith Winstein <mosh-devel@mit.edu>
-License: GPL-3+
+License: GPL-3+ with OpenSSL exception
  This program is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
@@ -18,6 +18,20 @@ License: GPL-3+
  You should have received a copy of the GNU General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.
  .
+ In addition, as a special exception, the copyright holders give
+ permission to link the code of portions of this program with the
+ OpenSSL library under certain conditions as described in each
+ individual source file, and distribute linked combinations including
+ the two.
+ .
+ You must obey the GNU General Public License in all respects for all
+ of the code used other than OpenSSL. If you modify file(s) with this
+ exception, you may extend this exception to your version of the
+ file(s), but you are not obligated to do so. If you do not wish to do
+ so, delete this exception statement from your version. If you delete
+ this exception statement from all source files in the program, then
+ also delete it here.
+ .
  On Debian systems, the complete text of the GNU General
  Public License version 3 can be found in "/usr/share/common-licenses/GPL-3".