Cabal man pages

Joey,

I convinced cabal to install the man page.  I'm surprised cabal does not have built-in support for this.

Along the way I refactored the generation of the git-annex.cabal.

I also added a .dir-locals.el that configures emacs to use tabs for indentation for files in the repo.  From the Makefile I infer that you're using vim, so this shouldn't affect you, and might be helpful to other emacs users that want to contribute, but have their emacs set up to use spaces for indentation.

Cheers,

-nathan