util to find different/missing forum users

Look for differences beween the LMS and Forum database user list.
Because doing this directly against models is offensively slow,
this just directly uses the MongoDB and MySQL Python drivers to
hit the databases directly and compare the lists.
fix recipient bug; no toArray() on aggreg result
Merge branch 'master' of github.com:Stanford-Online/dump-dbs

Conflicts:
	forum_user_audit.py