bug#24520: 25.1.50; calccard.tex has somewhat unclear licensing

[naesten]

Evaluate:

  (find-file (expand-file-name "refcards/calccard.tex" data-directory))

Now search for "Copyright" in the resulting buffer.  The first occurance
is as part of the usual GPLv3 boilerplate, just a bit further into the
file than is usual.  The second occurance precees a somewhat less clear
license grant:

> \def\copyrightnotice{
> \vskip 1ex plus 2 fill\begingroup\small
> \centerline{Copyright \copyright\ \year\ Free Software Foundation, Inc.}
> \centerline{designed by Dave Gillespie and Stephen Gildea,}
> \centerline{for GNU Emacs Calc.}
>
> Permission is granted to make and distribute copies of
> this card provided the copyright notice and this permission notice
> are preserved on all copies.
>
> %For copies of the GNU Emacs Calc manual, write to the Free Software
> %Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
> %MA 02110-1301, USA.
> %
> \endgroup}

So, we have two license grants that'd seem to apply to this file,

 (a) the usual GPLv3-or-later boilerplate
 
 (b) a brief, custom grant that doesn't explicitly permit modification

Also note that only (b) appears on the actual card; I don't think
there's even enough room on the card to fit (a).

Its not really clear what the licensing of this file is meant to be, but
I think it would be simplest to:

 (a) drop the GPLv3 licensing on this file, or explicitly use a dual
     license/GPL exception to unambiguously permit distribution with
     just the brief grant
    
 (b) add "in modified or unmodified form" to, and possibly remove "and
     this permission notice" from, said brief grant

 (c) mention the filename "calccard.tex" so people recieving it
     out-of-context can find the source easily

(Aside: the commented-out FSF address seems kind of useless nowadays...)

In GNU Emacs 25.1.50.1 (x86_64-w64-mingw32)
 of 2015-12-25
Repository revision: 9f0fd7cb1aec3eb9e2e0f7b8854c30870286d96c