Upgrade audio/snd to 15.7 and unbreak

[truckman]

Summary

Upgrade from 13.0 to 15.7. The tutorial is no longer
included.

Remove a dead mirror and add SourceForge to MASTER_SITES

Unmark broken now that the distfile is fetchable

Add LICENSE*

Test Plan

Build on FreeBSD 8.4, 9.3, 10.1 and 11.0, both amd64 and i386

[truckman]

audio/snd/Makefile

13–16 ↗

(On Diff #6254)

This part of the update is the reason that I'm requesting the review. The license resembles the Tck/Tk license, so I used the tcl85 Makefile as an example.

The is the text of the license:

Snd is a sound editor written by Bill Schottstaedt ([e-mail]).
Except where otherwise noted, it is Copyright 1996-2013 Bill Schottstaedt.

The authors hereby grant permission to use, copy, modify, distribute,
and license this software and its documentation for any purpose. No
written agreement, license, or royalty fee is required. Modifications
to this software may be copyrighted by their authors and need not
follow the licensing terms described here.

IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY
FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
ARISING OUT OF THE USE OF THIS SOFTWARE, ITS DOCUMENTATION, OR ANY
DERIVATIVES THEREOF, EVEN IF THE AUTHORS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT. THIS SOFTWARE
IS PROVIDED ON AN "AS IS" BASIS, AND THE AUTHORS AND DISTRIBUTORS HAVE
NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR
MODIFICATIONS.

[mat]

audio/snd/Makefile

13–16 ↗

(On Diff #6254)

Yeah, this looks all right to me, the important bits when a custom license is used is to get the PERMS right, I see no restrictions in this one.