Remove dependencies on Boost.StaticAssert. (#155)

Boost.StaticAssert has been merged into Boost.Config, so remove
the dependency.

CMakeLists.txt

@@ -35,7 +35,6 @@ target_link_libraries(boost_program_options
     Boost::iterator
     Boost::lexical_cast
     Boost::smart_ptr
-    Boost::static_assert
     Boost::throw_exception
     Boost::type_traits
   PRIVATE

build.jam

@@ -14,7 +14,6 @@ constant boost_dependencies :
     /boost/iterator//boost_iterator
     /boost/lexical_cast//boost_lexical_cast
     /boost/smart_ptr//boost_smart_ptr
-    /boost/static_assert//boost_static_assert
     /boost/throw_exception//boost_throw_exception
     /boost/type_traits//boost_type_traits ;
 

include/boost/program_options/detail/value_semantic.hpp

@@ -17,13 +17,15 @@ namespace boost { template<class T> class optional; }
 
 namespace boost { namespace program_options { 
 
+    namespace detail {
         extern BOOST_PROGRAM_OPTIONS_DECL std::string arg;
+    }
     
     template<class T, class charT>
     std::string
     typed_value<T, charT>::name() const
     {
-        std::string const& var = (m_value_name.empty() ? arg : m_value_name);
+        std::string const& var = (m_value_name.empty() ? detail::arg : m_value_name);
         if (!m_implicit_value.empty() && !m_implicit_value_as_text.empty()) {
             std::string msg = "[=" + var + "(=" + m_implicit_value_as_text + ")]";
             if (!m_default_value.empty() && !m_default_value_as_text.empty())

src/value_semantic.cpp

@@ -84,12 +84,14 @@ namespace boost { namespace program_options {
     }
 #endif
 
+    namespace detail {
         BOOST_PROGRAM_OPTIONS_DECL std::string arg("arg");
+    }
 
     std::string
     untyped_value::name() const
     {
-        return arg;
+        return detail::arg;
     }
     
     unsigned