doc: Update gpl.texi to match version from gnupg

--

Somehow the doc/gpl.texi from gpgme and gnupg drifted out of sync.
This patch to gpgme's file brings it in line with gnupg's master
branch, and avoids the following errors during make:

./gpl.texi:667: @section seen before @end enumerate
./gpl.texi:724: unmatched `@end enumerate'
./gpl.texi:1: warning: node next `Copying' in menu `Concept Index'
   and in sectioning `Function and Data Index' differ

doc/gpl.texi

@@ -1,4 +1,5 @@
 @node Copying
+
 @unnumbered GNU General Public License
 @center Version 3, 29 June 2007
 
@@ -11,7 +12,7 @@ Everyone is permitted to copy and distribute verbatim copies of this
 license document, but changing it is not allowed.
 @end display
 
-@section Preamble
+@unnumberedsec Preamble
 
 The GNU General Public License is a free, copyleft license for
 software and other kinds of works.
@@ -77,7 +78,7 @@ The precise terms and conditions for copying, distribution and
 modification follow.
 
 @iftex
-@section TERMS AND CONDITIONS
+@unnumberedsec TERMS AND CONDITIONS
 @end iftex
 @ifinfo
 @center TERMS AND CONDITIONS
@@ -227,7 +228,7 @@ terms of section 4, provided that you also meet all of these
 conditions:
 
 @enumerate a
-@item 
+@item
 The work must carry prominent notices stating that you modified it,
 and giving a relevant date.
 
@@ -658,13 +659,16 @@ an absolute waiver of all civil liability in connection with the
 Program, unless a warranty or assumption of liability accompanies a
 copy of the Program in return for a fee.
 
+@end enumerate
+
 @iftex
 @heading END OF TERMS AND CONDITIONS
 @end iftex
 @ifinfo
 @center END OF TERMS AND CONDITIONS
 @end ifinfo
-@section How to Apply These Terms to Your New Programs
+
+@unnumberedsec How to Apply These Terms to Your New Programs
 
 If you develop a new program, and you want it to be of the greatest
 possible use to the public, the best way to achieve this is to make it
@@ -674,9 +678,11 @@ terms.
 To do so, attach the following notices to the program.  It is safest
 to attach them to the start of each source file to most effectively
 state the exclusion of warranty; and each file should have at least
-the ``copyright'' line and a pointer to where the full notice is found.
-@smallexample
-@var{one line to give the program's name and a brief idea of what it does.}  
+the ``copyright'' line and a pointer to where the full notice is
+found.
+
+@example
+@var{one line to give the program's name and a brief idea of what it does.}
 Copyright (C) @var{year} @var{name of author}
 
 This program is free software: you can redistribute it and/or modify
@@ -691,17 +697,21 @@ General Public License for more details.
 
 You should have received a copy of the GNU General Public License
 along with this program.  If not, see @url{http://www.gnu.org/licenses/}.
-@end smallexample
+@end example
 
+@noindent
 Also add information on how to contact you by electronic and paper mail.
 
+@noindent
 If the program does terminal interaction, make it output a short
 notice like this when it starts in an interactive mode:
 
 @smallexample
-@var{program} Copyright (C) @var{year} @var{name of author} 
-This program comes with ABSOLUTELY NO WARRANTY; for details type @samp{show w}.
-This is free software, and you are welcome to redistribute it under certain conditions; type @samp{show c} for details.
+@var{program} Copyright (C) @var{year} @var{name of author}
+This program comes with ABSOLUTELY NO WARRANTY; for details
+type @samp{show w}.  This is free software, and you are
+welcome to redistribute it under certain conditions;
+type @samp{show c} for details.
 @end smallexample
 
 The hypothetical commands @samp{show w} and @samp{show c} should show
@@ -720,5 +730,3 @@ library, you may consider it more useful to permit linking proprietary
 applications with the library.  If this is what you want to do, use
 the GNU Lesser General Public License instead of this License.  But
 first, please read @url{http://www.gnu.org/philosophy/why-not-lgpl.html}.
-
-@end enumerate