Drop database connections before forking

If we drop the database connections before the fork, they all get reestablished properly afterward.

Tested on `rflow_examples/rails3` - spun up 10 processes (and database pool was only 5 connections), hit it with `ab -n 1000 -c 100 "http://127.0.0.1:8000/"`, had no problems.

Fixes issues where newly started workers couldn't save stuff to the database. See also #13.