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

flower/include/memory-stream.hh

 /*
   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/>.
 */
 
 #ifndef MEMORY_STREAM_HH
 #define MEMORY_STREAM_HH
 
 #include <cstdio>
 #include <unistd.h>
-using namespace std;
 
 #include "libc-extension.hh"
 #include "file-cookie.hh"
 
 class Memory_out_stream
 {
   char *buffer_;
   ssize_t size_;
   int buffer_blocks_;
   FILE *file_;
 
   static lily_cookie_io_functions_t functions_;
   static const int block_size_;
 
 public:
   static ssize_t reader (void *, char *, size_t);
   static ssize_t writer (void *, char const *, size_t);
   static ssize_t seeker (void *, off64_t *, size_t);
   static ssize_t cleaner (void *);
 
   Memory_out_stream ();
   ~Memory_out_stream ();
   FILE *get_file () const;
   char const *get_string () const;
   ssize_t get_length () const;
 };
 
 #endif /* MEMORY_STREAM_HH */