Refactored `Ember.Route`s teardown mechanism for rendered views. This fixes #2857, previously multiple outlets were not tore down.
Merge pull request #2873 from Batterii/workmanw/fix-tearing-down-multiple-outlets

Improved `Ember.Route`s teardown mechanism for rendered views.

Prior to this commit, if multiple `render` calls were made in `renderTemplate`, only the last was torn down.