[boost] [thread_safe_signals] returning void from last_value when possible

Hello, When dealing with a signature of void return type, the Boost.Signals version of last_value only returns last_value::unusable when the compiler doesn't support void returns: http://svn.boost.org/trac/boost/browser/trunk/boost/last_value.hpp#L34 But the thread-safe version always returns last_value::unusable: http://svn.boost.org/trac/boost/browser/sandbox/thread_safe_signals/boost/la... Could the thread-safe version be made consistent with Boost.Signals? Thanks, Stjepan