Prepare for newrelic 3.0.

! Incompatible change in Newrelic 3.0.
  Please update your copy of 04_newrelic.ini from the sample provided.
- Tweaked stock newrelic.cfg.
- NR related scripts and daemon will only run if env var
  `NEW_RELIC_LICENSE_KEY` is defined and that the 3.0 package specific
  `NEWRELIC_VERSION` file exists in /app/local/newrelic.
Bundle PHP newrelic agent extension and deploy on slugc.
Newrelic version: 3.7.5.7.

Closes #8.