All Database usage must go through framework.db (which should have been
the case before, anyways) or explicitly checkout and checkin a
connection. Failure to do so causes thread starvation and bizarre
random failures when attempting to use the database.
This commit also explicitly releases database connections at the end of
all threads created via framework.threads.spawn, which should alleviate
Deprecation Warning messages from ActiveRecord.
[Fixes#6613]
James Lee
876c59b192