[boost] patch to build boost on dragonflybsd

the attached patch makes it possible to build boost on dragonflybsd with gcc3.4. the change in boost/python/detail/config.hpp is necessary as dfly doesn't provide the gcc-patched headers that "fix" offsetof(). if defined(freebsd)&&!defined(dragonfly) is in there as dfly sometimes defines both of them. after this patch, everything except boost::serialize (which complains about lack of wchar_t) should build. patrick mauritz