yesod-default is needed as a dependancy

Seems like there is a needed dependancy, yesod-default is needed on OSX.

Utility/Yesod.hs:10:8:
    Could not find module `Yesod.Default.Util'
    Use -v to see a list of the files searched for.
make: *** [git-annex] Error 1

Only on OSX apparently. Weird. Added. done --Joey