windows builders need libmemcached workaround

libmemcached doesn't build automatically on win buildslaves via wallace buildbot.

however, libmemcached does build via manual wallace.

the paths might be too long for windows o/s?

so, for now, I've copied the manually built wallace libmemcached artifacts to wallace buildbot locations, as a workaround.

this is a hack while under date pressure. libmemcached is slowly changing, but this will break when we ever get around to upgrading to the latest libmemcached.