title: using gzip_compressor with boost::iostreams::filtering_wostream, compiler error
body: <p>Code snippet below compiles fine with string but not with <code>&lt;wstring&gt;</code>.</p>
  
  <p>I used <code>filtering_ostream</code> with <code>&lt;string&gt;</code></p>
  
  <pre><code>const void X::Compress(const wstring&amp; data)
  {
      wstring compressedString;
      boost::iostreams::filtering_wostream compressingStream;
      compressingStream.push(boost::iostreams::gzip_compressor(boost::iostreams::gzip_params(boost::iostreams::gzip::best_compression)));
      compressingStream.push(boost::iostreams::back_inserter(compressedString));
      compressingStream &lt;&lt; data;
      boost::iostreams::close(compressingStream);
  
      //...
  }
  </code></pre>
  
  <p>Compilation error:</p>
  
  <pre><code>\boost_x64/boost/iostreams/chain.hpp:258:9: error: no matching function for call to std::list&lt;boost::iostreams::detail::linked_streambuf&lt;wchar_t, std::char_traits&lt;wchar_t&gt; &gt;*, 
  std::allocator&lt;boost::iostreams::detail::linked_streambuf&lt;wchar_t, std::char_traits&lt;wchar_t&gt; &gt;*&gt; &gt;::push_backn(std::auto_ptr&lt;boost::iostreams::stream_buffer&lt;boost::iostreams::basic_gzip_compressor&lt;&gt;, std::char_traits&lt;wchar_t&gt;, std::allocator&lt;wchar_t&gt;, boost::iostreams::output&gt; &gt;::element_type*)
           list().push_back(buf.get());
       ^
  </code></pre>