Use maintained version of clojure.java.jdbc

There are some updates to the maintained version of `clojure.java.jdbc` that would be nice to use with Korma (Korma is currently using `clojure.java.jdbc.deprecated`).

This addresses issue https://github.com/korma/Korma/issues/207
Maybe "(if *current-conn*" could change to:
  (if (identical? *current-conn* (or db @_default *current-conn*))
to check if the default or entities db needed to be used.