be more precise why files are in the public-domain

As per [1], "License: public-domain" needs an explanation why the work
is in the public-domain.

[1] https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/

Signed-off-by: Marco van Wieringen <marco.van.wieringen@bareos.com>

debian/copyright

@@ -1247,12 +1247,25 @@ License: BSD-3-clause
 Files: src/lib/md5.h src/lib/md5.c
 Copyright: 2001 Alexander Peslyak
 License: public-domain
+ This software was written by Alexander Peslyak in 2001.  No copyright is
+ claimed, and the software is hereby placed in the public domain.
+ In case this attempt to disclaim copyright and place the software in the
+ public domain is deemed null and void, then the software is
+ Copyright (c) 2001 Alexander Peslyak and it is hereby released to the
+ general public under the following terms:
+ .
+ Redistribution and use in source and binary forms, with or without
+ modification, are permitted.
+ .
+ There's ABSOLUTELY NO WARRANTY, express or implied.
+ .
+ (This is a heavily cut-down "BSD license".)
 
 
 Files: src/lib/sha1.h src/lib/sha1.c
 Copyright: Steve Reid <steve@edmweb.com>
 License: public-domain
-
+ This work was put by the author in the public domain.
 
 Files: src/lib/var.h src/lib/var.c
 Copyright: 2001-2002 Ralf S. Engelschall <rse@engelschall.com>

debian/copyright.footer

@@ -123,12 +123,25 @@ License: BSD-3-clause
 Files: src/lib/md5.h src/lib/md5.c
 Copyright: 2001 Alexander Peslyak
 License: public-domain
+ This software was written by Alexander Peslyak in 2001.  No copyright is
+ claimed, and the software is hereby placed in the public domain.
+ In case this attempt to disclaim copyright and place the software in the
+ public domain is deemed null and void, then the software is
+ Copyright (c) 2001 Alexander Peslyak and it is hereby released to the
+ general public under the following terms:
+ .
+ Redistribution and use in source and binary forms, with or without
+ modification, are permitted.
+ .
+ There's ABSOLUTELY NO WARRANTY, express or implied.
+ .
+ (This is a heavily cut-down "BSD license".)
 
 
 Files: src/lib/sha1.h src/lib/sha1.c
 Copyright: Steve Reid <steve@edmweb.com>
 License: public-domain
-
+ This work was put by the author in the public domain.
 
 Files: src/lib/var.h src/lib/var.c
 Copyright: 2001-2002 Ralf S. Engelschall <rse@engelschall.com>