Capitalization in the title of the section, enumerates the environments
in the usual order, adds a paragraph, and tries to use less "you"s.

Proxy servers add X-Forwarded-For headers, resulting in a list of IPs. We
remove trusted IP values, and then take the last given value, assuming that
it is the most likely to be the correct, unfaked value. See [1] for a very
thorough discussion of why that is the best option we have at the moment.

[1]: http://blog.gingerlime.com/2012/rails-ip-spoofing-vulnerabilities-and-protection/

Fixes #7979

This can be done using the class attribute cache_timestamp_format

Conflicts:
	railties/guides/source/configuring.textile

There's no reason for guides to reference old behaviors. They should
be current as of the versions of Rails that they ship with, and including
older information just clutters thing.

I discussed this change with @fxn and he agrees.

We have three or four different introduction sentences to the guides.
After this commit, we use the same one everywhere.

Talked with @fxn about this. Bullet points should have periods at the ends.

They was extracted from a plugin.

See https://github.com/rails/rails-observers

[Rafael Mendonça França + Steve Klabnik]

Also remove references for RAILS_ASSET_ID from the guides

[ci skip]

Removed the asset_path configuration from the guides and added an entry
in the upgrading_ruby_on_rails guide

[ci skip]

This reverts commit f5b9ed4f.

REASON: Translation work can not be done in the docrails repository

This option is now unsupported in sprockets-rails.

Date.beginning_of_week thread local and beginning_of_week application config option added (default is Monday)

erb tag wasn't closed well