Monitorable object & snapshot: Add information about exceptions thrown when updating metrics

In case an exception is thrown by a retrieveMetricValues method, the following information will be stored in MonitorableObjectSnapshot:

• The exception type
• The exception message
• The function, file and line from which the exception was thrown
• All of the above for a nested exception, in case one throws a new exception from a catch block and stores the previous exception as follows:

void my_internal_function()
{
  MyException e("some message");

  boost::throw_exception(MyException("blah"))\
    << ::boost::original_exception_type(&typeid(e))\
    << ::boost::throw_function(BOOST_CURRENT_FUNCTION)\
    << ::boost::throw_file(__FILE__)\
    << ::boost::throw_line((int)__LINE__);
}

void my_function()
{
  try {
    my_internal_function();
  }
  catch (boost::exception& e) {
    const boost::exception_ptr lEPtr = boost::current_exception();
    throw MyException2()\
      << ::boost::throw_function(BOOST_CURRENT_FUNCTION)\
      << ::boost::throw_file(__FILE__)\
      << ::boost::throw_line((int)__LINE__)\
      << (boost::errinfo_nested_exception(lEPtr));
  }
}

Note: May need to update the SWATCH_THROW macro in the future to be able to extract messages from nested exceptions correctly.