Upgrade system and filesystem to conform system_category and generic_category interface to N3090, the current C++0x working paper, section 19.5, System error support.

Refactor API macros into a new header, boost/system/api_config.hpp.

Prohibit user definition of API macros. Rationale: ensure all translation units use same definitions, cut number of environments that need to be tested.

[SVN r62313]

test/throw_test.cpp

@@ -25,7 +25,7 @@ namespace boost
   {
     BOOST_SYSTEM_DECL void throw_test()
     {
-      throw system_error(9999, get_system_category(), "boo boo");
+      throw system_error(9999, system_category(), "boo boo");
     }
   }
 }