- removed all Doom Source license and all default Raven copyright headers and replaced them with GPLv3. Also fixed the license in a few other files.

For some files that had the Doom Source license attached but saw heavy external contributions over the years I added a special note to license all original ZDoom code under BSD.

src/s_sndseq.cpp

@@ -1,13 +1,24 @@
-//**************************************************************************
-//**
-//** sn_sonix.c : Heretic 2 : Raven Software, Corp.
-//**
-//** $RCSfile: sn_sonix.c,v $
-//** $Revision: 1.17 $
-//** $Date: 95/10/05 18:25:44 $
-//** $Author: paul $
-//**
-//**************************************************************************
+//-----------------------------------------------------------------------------
+//
+// Copyright 1994-1996 Raven Software
+// Copyright 1999-2016 Randy Heit
+// Copyright 2002-2016 Christoph Oelckers
+//
+// 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
+// (at your option) any later version.
+//
+// This program 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/
+//
+//-----------------------------------------------------------------------------
+//
 
 #include <string.h>
 #include <stdio.h>