dmwm/DAS — pull request #4118 by vidma (2014-01-13 13:44:53+00:00)
Title: fix to correctly identify system special key

* fixes issue #4086 . earlier the query interpretation/parsing was failing in service_apis_map()
* this was caused by self.services(query) returning empty list of "available services"
- it expected str only, but got unicode in query.get('system', None)
- solution: use basestring instead of str