handle void return types on broken compilers

svn path=/branches/void_returns/boost/boost/bind.hpp; revision=11668
more void returns

svn path=/branches/void_returns/boost/boost/bind.hpp; revision=11672
suppress unused variable warning

svn path=/branches/void_returns/boost/boost/bind.hpp; revision=11673
Added copyright

svn path=/branches/void_returns/boost/boost/bind.hpp; revision=11675