Fix postgresql pulse, add default pulse path, and refactorings

I tried adding pulse to a postgresql app recently, and it failed because the `dual` table didn't exist. This seems to be a mysql thing, based on my poking around.

The action was pretty hard to read, with some duplication, and ambiguity of what was actually being checked for what adapter. Hopefully, this reads a lot better, and it's more obvious what to do for adding other adapters.

I also added a default pulse path, ie /pulse, since that is what we end up using 99% of the time.

While testing, also found the init.rb was not working.

What I've tested against, and is working:

* Rails 3.2 w/ mysql2
* Rails 3.2 w/ pg
* Rails 3.2 w/ sqlite3
* Rails 2.3 w/ mysql