Clarify effective GPLv3 licensing

While man-db's own files are individually licensed under GPLv2 (or in a
few cases LGPLv2.1), the project as a whole is effectively GPLv3 due to
Gnulib.  This was already explained in README.md, but make it a bit
clearer by having the top-level COPYING file be a copy of GPLv3.

* COPYING: Move to ...
* COPYING.GPLv2: ... here.
* COPYING: New file.
* Makefile.am (dist_noinst_DATA): Add COPYING.GPLv2.
* lib/README, man/it/man1/apropos.man1, man/it/man1/man.man1,
man/it/man1/manpath.man1, man/it/man1/whatis.man1,
man/it/man1/zsoelim.man1, man/it/man5/manpath.man5,
man/it/man8/accessdb.man8, man/it/man8/catman.man8,
man/it/man8/mandb.man8, man/man1/apropos.man1, man/man1/lexgrog.man1,
man/man1/man-recode.man1, man/man1/man.man1, man/man1/manconv.man1,
man/man1/manpath.man1, man/man1/whatis.man1, man/man1/zsoelim.man1,
man/man5/manpath.man5, man/man8/accessdb.man8, man/man8/catman.man8,
man/man8/mandb.man8, manual/comp.me, manual/db.me, manual/files.me,
manual/format.me, manual/glossary.me, manual/intro.me, manual/leader.me,
manual/man_db.me, manual/misc.me, manual/sec.me: Refer to COPYING.GPLv2
rather than COPYING.

1 files changed, 1 insertions, 1 deletions

diff --git a/man/man1/manconv.man1 b/man/man1/manconv.man1
index af1e3b30..4ae76a81 100644
--- a/man/man1/manconv.man1
+++ b/man/man1/manconv.man1
@@ -3,7 +3,7 @@
 .\" Copyright (c) 2007, 2008 Colin Watson <cjwatson@debian.org>
 .\"
 .\" You may distribute under the terms of the GNU General Public
-.\" License as specified in the file COPYING that comes with the
+.\" License as specified in the file COPYING.GPLv2 that comes with the
 .\" man-db distribution.
 .pc
 .TH %thmanconv% 1 "%date%" "%version%" "Manual pager utils"