Specify once_temp_type dtor with noexcept(false)

This addresses issues due to C++11 changes pointed some time ago by Roger Orr (http://sourceforge.net/mailarchive/message.php?msg_id=26451676).
Fixes #181.
Merge pull request #192 from mloskot/core-noexcept

Specify once_temp_type dtor with noexcept(false)