Resolved T3382 - Oh noes guy flashing

Summary:
Although we cancelled the timeout to show oh-noes-guy when hide() was called,
timeouts could hang around if they were superseded by another call to toggleErrors()
without calling hide in between. These stragglers would fire later on and create the
effect of oh-noes0guy flickering

Test Plan:
- Watch the talkie mentioned in the task
- Don't see flickering

Reviewers: pamela, john

Subscribers: #cs

Differential Revision: http://phabricator.khanacademy.org/D14676