This is not a recommended way to install git-annex. Use HomeBrew or the prebuilt app bundle instead.
But if you really want to use MacPorts:
Install the Haskell Platform from http://hackage.haskell.org/platform/mac.html. The version provided by Macports is too old to work with current versions of git-annex. Then execute
sudo port install git ossp-uuid md5sha1sum coreutils gnutls libxml2 libgsasl pkgconfig sudo cabal update PATH=$HOME/bin:$PATH cabal install c2hs git-annex --bindir=$HOME/bin
Do not forget to add to your PATH variable your ~/bin folder. In your .bashrc, for example: