Clarify that only these specific files are GPLv2 or v3.

Icecast itself remains GPLv2 only.

svn path=/icecast/branches/icecast-webm/; revision=18307

src/format_ebml.c

 /* Icecast
  *
  * This program is distributed under the GNU General Public License,
- * version 2, or later. A copy of this license is included with this source.
+ * version 2. A copy of this license is included with this source.
+ * At your option, this specific source file can also be distributed
+ * under the GNU GPL version 3.
  *
  * Copyright 2012,      David Richards, Mozilla Foundation,
  *                      and others (see AUTHORS for details).

src/format_ebml.h

 /* Icecast
  *
  * This program is distributed under the GNU General Public License,
- * version 2 or later. A copy of this license is included with this source.
+ * version 2. A copy of this license is included with this source.
+ * At your option, this specific source file can also be distributed
+ * under the GNU GPL version 3.
  *
  * Copyright 2012,      David Richards, Mozilla Foundation,
  *                      and others (see AUTHORS for details).

src/format_opus.c

 /* Icecast
  *
  *  This program is distributed under the GNU General Public License,
- *  version 2 or later. A copy of this license is included with this source.
+ *  version 2. A copy of this license is included with this source.
+ *  At your option, this specific source file can also be distributed
+ *  under the GNU GPL version 3.
  *
  * Copyright 2012,      David Richards, Mozilla Foundation,
  *                      and others (see AUTHORS for details).

src/format_opus.h

 /* Icecast
  *
  * This program is distributed under the GNU General Public License,
- * version 2 or later. A copy of this license is included with this source.
+ * version 2. A copy of this license is included with this source.
+ * At your option, this specific source file can also be distributed
+ * under the GNU GPL version 3.
  *
  * Copyright 2012,      David Richards, Mozilla Foundation,
  *                      and others (see AUTHORS for details).