Switching the Cygwin DLL to LGPLv3+, dropping commercial buyout option

Bump GPLv2+ to GPLv3+ for some files, clarify BSD 2-clause.

Everything else stays under GPLv3+.

New Linking Exception exempts resulting executables from LGPLv3 section 4.

Add CONTRIBUTORS file to keep track of licensing.

Remove 'Copyright Red Hat Inc' comments.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygserver/cygserver-config

@@ -1,7 +1,5 @@
 #!/bin/bash
 #
-# cygserver-config, Copyright 2003 Red Hat Inc.
-#
 # This file is part of the Cygwin DLL.
 
 # Directory where the config files are stored