Issue 4550: Avoid "using namespace std;" in included files (Take 2)

lily/volta-bracket.cc

 /*
   This file is part of LilyPond, the GNU music typesetter.
 
   Copyright (C) 1997--2020 Jan Nieuwenhuizen <janneke@gnu.org>
 
   LilyPond is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.
 
   LilyPond is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
 
   You should have received a copy of the GNU General Public License
   along with LilyPond.  If not, see <http://www.gnu.org/licenses/>.
 */
 
 #include <cstring>
-using namespace std;
 
 #include "warn.hh"
 #include "font-interface.hh"
 #include "line-interface.hh"
 #include "paper-column.hh"
 #include "output-def.hh"
 #include "text-interface.hh"
 #include "volta-bracket.hh"
 #include "pointer-group-interface.hh"
 #include "side-position-interface.hh"
 #include "directional-element-interface.hh"
 #include "lookup.hh"
 #include "bracket.hh"
 #include "lily-imports.hh"
 
+using std::string;
+
 /*
   this is too complicated. Yet another version of side-positioning,
   badly implemented.
 
   --
 
   * Should look for system_start_delim to find left edge of staff.
   */
 
 MAKE_SCHEME_CALLBACK (Volta_bracket_interface, print, 1);
@@ skipping 119 matching lines @@
                "Volta bracket with number.",
 
                /* properties */
                "bars "
                "dashed-edge "
                "height "
                "shorten-pair "
                "thickness "
               );