268 datastore setup instructions don't work

Corresponding issue: <https://github.com/okfn/ckan/issues/268>

@amercader @domoritz Suggest one of you probably wants to review this

What I'm trying to do here is make it so that if someone follows the source install instructions and then the datastore setup instructions and just copy-pastes all the commands, and just uncomments the lines from the default ini file without changing them, everything should work. Currently it's not the case but I think this pull request mostly fixes it.

I also tried to move unnecessary waffle, keep it short and sweet, people just want datastore to work asap (from a CKAN user's point of view, it's infuriating that CKAN doesn't just "store data" by default without needing any further setup, since they do need further setup let's try and keep it as short and simple as possible)

This can be reviewed not but **let's not merge this one quite yet**, I'd like to wait for an answer to [this email thread](http://lists.okfn.org/pipermail/ckan-dev/2013-January/003695.html), and also to test stepping through the source install instructions followed by the new datastore setup instructions on a fresh Ubuntu VM to make sure there are no more problems.