[boost] [reference_wrapper] add operator()(Args...) to reference_wrapper

Given that Boost now has perfect forwarding emulation through Boost.Move and a better result_of, would it be possible to enable reference_wrapper to forward the function call operator? The current behavior is somewhat surprising and makes a few of the most promising applications of reference_wrapper (reference wrap polymorphic boost::function objects) impossible with code that is no prepared to work with reference_wrapper. It would also be more consistent with reference_wrapper of the stdlib. I can file a corresponding bug report and add a patch, if there is interest. Cheers, Philipp Moeller