Don't use the absolute path to the bindist tarball

On Windows, we end up doing something like
    rsync c:/build/ghc-6.10.1-unknown-mingw32.tar.bz2 haskell.org:dist
and it thinks that it is meant to get the file from the host called "c".
Now we just do
    rsync ghc-6.10.1-unknown-mingw32.tar.bz2 haskell.org:dist
so rsync understand what we mean.