Add clarifying comment to melange.models.User for account_id.
Add clarifying comment to melange.models.User for account_id.

Addresses the (formerly) implicit expectation that account_id be
assigned to User.user_id() where User is the current AppEngine user.

rhyolight/nupic.son,rhyolight/nupic.son,rhyolight/nupic.son