Major upgrade to Boost.Config symbol visibility macros for shared libraries, based on patches from Jürgen Hunold with mods by Beman Dawes. Upgrade Boost.System to use the new visibility macros. Fixes #3697 and provides foundation for fixing 2114, 2309, etc.

[SVN r62140]

include/boost/system/system_error.hpp

@@ -17,9 +17,11 @@ namespace boost
 {
   namespace system
   {
-    //  class system_error  --------------------------------------------------//
+    //  class system_error  ------------------------------------------------------------//
 
-    class system_error : public std::runtime_error
+    class BOOST_SYMBOL_VISIBLE system_error : public std::runtime_error
+    // BOOST_SYMBOL_VISIBLE is needed by GCC to ensure system_error thrown from a shared
+    // library can be caught. See svn.boost.org/trac/boost/ticket/3697 
     {
     public:
       system_error( error_code ec )