Include binstubs generated by Rails 4

Commit b516ecc added `bin/` to the .gitignore file. Now that Discourse
runs using Rails 4 by default, however, we should include the binstubs
generated by `rake rails:update:bin` in version control as this is the
recommendation of the Rails core team. Additionally, for those wishing
to deploy Discourse to Heroku, these binstubs are actually mandatory
according to [this article](https://devcenter.heroku.com/articles/rails4).

Other binstubs can continue to be ignored.

Signed-off-by: David Celis <me@davidcel.is>
Refactors TopicCreator
Default values for posts/topics fields on Category

When creating categories (or, at least, subcategories), certain integer
values are set to a default of NULL: topics_week, topics_month,
topics_year, posts_week, posts_month, and posts_year. This causes
consistent exceptions when trying to visit `/categories`, with the
offending line being in
`CategoryDetailedSerializer#count_with_subcategories`. This attempts to
coerce nil into Fixnum.

A fix could be to convert to 0 in the code, but these attributes should
really never be NULL. If there are no posts or topics, they should be 0
to maintain data integrity.

Signed-off-by: David Celis <me@davidcel.is>
new intro message and better 404 copy
Merge pull request #1914 from velesin/topic_creator_refactoring

Refactors TopicCreator
Version bump to v0.9.8.4
Update new_user top page redirect reason

The goal of this text is to sublty hint that reading is the way to graduate out of it.
FEATURE: proper mailing list mode

once enable_mailing_list_mode is enabled any user can elect
to get every post via email unless they opt out of category or topic
Update annotations
Don't notify about dominating private messages.
BUGFIX: scheduler crash in blocking_tick
Merge pull request #1915 from riking/patch-2

Update new_user top page redirect reason
BUGFIX: plugins not updating after assets:precompile

Now that we have a fancy cache we can nuke all old assets
This is way better cause it ensures all .erbs get re-evaluated
And ensures plugins are updated
SECURITY: check permissions for mailing list

if you deployed this feature in the last 2 hours upgrade asap.
SECURITY: reduce moderator rights

You can now hide particular categories from certain moderators
SECURITY: dissalow mods from seeing PMs
another try fixing this test
fixing watermark/gutter link interference, and also adding a transition to the topic-progress bar, so smooth!
Merge pull request #1917 from awesomerobot/master

fixing watermark/gutter link interference
Merge pull request #1916 from vikhyat/pm-dominating

Don't notify about dominating private messages