Avoid deprecated bind placeholders in global namespace

This fixes numerous compilation warnings:

  note: #pragma message:
    The practice of declaring the Bind placeholders (_1, _2, ...)
    in the global namespace is deprecated.
    Please use <boost/bind/bind.hpp> + using namespace boost::placeholders,
    or define BOOST_BIND_GLOBAL_PLACEHOLDERS to retain the current behavior.

src/cmdline.cpp

@@ -15,7 +15,7 @@
 #include <boost/program_options/positional_options.hpp>
 #include <boost/throw_exception.hpp>
 
-#include <boost/bind.hpp>
+#include <boost/bind/bind.hpp>
 
 #include <string>
 #include <utility>
@@ -29,6 +29,8 @@
 
 #include <iostream>
 
+using namespace boost::placeholders;
+
 namespace boost { namespace program_options {
 
     using namespace std;

src/convert.cpp

@@ -19,9 +19,10 @@
 #include <boost/program_options/detail/utf8_codecvt_facet.hpp>
 #include <boost/throw_exception.hpp>
 
-#include <boost/bind.hpp>
+#include <boost/bind/bind.hpp>
 
 using namespace std;
+using namespace boost::placeholders;
 
 namespace boost { namespace detail {
 

src/parsers.cpp

@@ -16,7 +16,7 @@
 #include <boost/program_options/environment_iterator.hpp>
 #include <boost/program_options/detail/convert.hpp>
 
-#include <boost/bind.hpp>
+#include <boost/bind/bind.hpp>
 #include <boost/throw_exception.hpp>
 
 #include <cctype>
@@ -61,6 +61,7 @@ extern char** environ;
 #endif
 
 using namespace std;
+using namespace boost::placeholders;
 
 namespace boost { namespace program_options {