Cannot read negative time_duration

[damienrg+bug@…]

Loading a negative time_duration saved with operator<< does not work.

Test program:

#include <cassert>
#include <sstream>

#include <boost/date_time.hpp>

int main()
{
  boost::posix_time::time_duration expected(0, 0, 0, -1);
  std::stringstream stream;
  stream << expected;
  boost::posix_time::time_duration time;
  stream >> time;
  assert(expected == time);
  return 0;
}