fix. error importing UserMetricError, use base Exception class.
mod. use http://noc.wikimedia.org/conf/ dblists to build project : db map.
fix. don't need to check concurrent jobs to add to wait queue.
fix. When project as a function of cohort tag  from url is invalid use whatever is passed in the request.
fix. ensure that user IDs are strings so they can be matched.
Merge pull request #21 from rfaulkner/working

Fixes for WEP_AR to build cohort composites and other misc