Added errinfo_nested_exception typedef. Fixed minor documentation error.

[SVN r56766]

test/Jamfile.v2

@@ -59,4 +59,5 @@ compile errinfo_errno_hpp_test.cpp ;
 compile errinfo_file_handle_hpp_test.cpp ;
 compile errinfo_file_name_hpp_test.cpp ;
 compile errinfo_file_open_mode_hpp_test.cpp ;
+compile errinfo_nested_exception_hpp_test.cpp ;
 compile errinfo_type_info_name_hpp_test.cpp ;