bug 822759 - fixes for enabling the metlog client @ settings.METLOG

* switched settings back to having METLOG_CONF set in one place
* bumped django-raven-metlog and metlog-raven revisions for more
  consistent configuration
* renamed USE_METLOG_FOR_RAVEN to USE_METLOG_FOR_TASTYPIE for clarity
* enabled tastypie logging through metlog
* set the SENTRY_CLIENT so that all raven messages are routed through
  metlog
* removed the dual loggers in the explode() function of generate-error.  Just use the one true logger in settings.METLOG