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

lily/file-name-map.cc

 /*
   This file is part of LilyPond, the GNU music typesetter.
 
   Copyright (C) 2005--2020 Han-Wen Nienhuys <hanwen@xs4all.nl>
 
   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 <map>
-using namespace std;
 
 #include "file-name-map.hh"
 #include "lily-guile.hh"
 
+using std::map;
+using std::string;
+
 map<string, string> file_name_map_global;
 
 string
 map_file_name (const string &s)
 {
   if (file_name_map_global.find (s) != file_name_map_global.end ())
     return file_name_map_global[s];
   return s;
 }
 
 LY_DEFINE (ly_add_file_name_alist, "ly:add-file-name-alist",
            1, 0, 0, (SCM alist),
            "Add mappings for error messages from @var{alist}.")
 {
   for (SCM s = alist; scm_is_pair (s); s = scm_cdr (s))
     {
       SCM key = scm_caar (s);
       SCM val = scm_cdar (s);
 
       file_name_map_global[ly_scm2string (key)] = ly_scm2string (val);
     }
   return SCM_UNSPECIFIED;
 }