s/nexts/these (nexts is not a word)

tidied up a little and clarified
Merge pull request #2428 from gilesbowkett/copyedit_in_contributing

copy edits only: s/nexts/these (nexts is not a word)
Add homepage example test
Merge pull request #2435 from teddyzeenny/homepage-test

Add homepage example test
Actually make Ember.alias() print deprecation warnings.
Merge pull request #2445 from eventualbuddha/actually-deprecate-ember-alias

Actually make Ember.alias() print deprecation warnings.