Update apache tunings based on research.

- KeepAliveTimeout 2 => allows plenty of time for main page load to use
  KeepAlive while recycling the connection for others as quickly as
  possible.
- ThreadStackSize => drop to 1MB (default on linux is 8MB) to reduce
  memory used per mpm_worker thread. Really helps on low-memory boxes,
  and heroku dynos allow only 512MB.