* added support to moz_metlog client to support the STATSD_PREFIX in django settings
* forced the use of django < 1.5 for travis
* require STATSD_PREFIX to be defined with the moz_metlog client
* removed check for self._prefix from moz_metlog
* cleanups in the testcases to use Django TestCase to clobber settings
* bumped revision to 0.3.8.6