Some boost versions have a conflicting public overload of wait_until that returns void. Explicitly use a template here to avoid hitting that overload.

Tested against boost 1.52, which is confirmed broken -> fixed.

For reference, here are the competing overloads (from thread/pthread/condition_variable_fwd.hpp):

        template <class Duration>
        cv_status
        wait_until(
                unique_lock<mutex>& lock,
                const chrono::time_point<chrono::system_clock, Duration>& t)
        {
...
        inline void wait_until(
            unique_lock<mutex>& lk,
            chrono::time_point<chrono::system_clock, chrono::nanoseconds> tp)
        {

boost::chrono::system_clock::duration is typedef'd as chrono::nanoseconds, so without template params we end up falling into the void-return overload.