refactor the naming within plugin new generator

Having a method called `full?`, which checks on :full and :mountable
is very confusing. I renamed `full?` to `engine?` and created a `full?`
method that only checks the `:full` option
Changelog improvements [ci skip]
Restore original remote_ip algorithm.

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
Merge pull request #7980 from steveklabnik/issue_7979

Restore original remote_ip algorithm.
Explain the possible precautions
Merge pull request #8706 from steveklabnik/ip_precautions

Explain the possible IP precautions
Pass in `--local` when doing `gem install` for local gems.
refactor Routing::Mapper
test PATCH method for update action in generated scaffold controller test rather than PUT
Merge pull request #8714 from utkarshkukreti/faster-gem-install

Pass in `--local` when doing `gem install` for local gems. [ci skip]
Merge pull request #8715 from goshakkk/refactor-mapper

Refactor Routing::Mapper#matches?
Merge pull request #8717 from amatsuda/scaffold_controller_test_patch

test PATCH method for update action in generated scaffold controller test rather than PUT
Fix typo on form_tag_helper.rb

The inline documentantion had a typo that was somewhat confusing.
Merge pull request #8719 from pcasaretto/fix-actionview-doc-typo

Fix typo on form_tag_helper.rb [ci skip]
fix env toggling, improve error page styling
Merge pull request #8713 from goshakkk/better-error-page

Fix env toggling, improve error page styling
Typo and grammar fixes in the ActionPack CHANGELOG
Merge pull request #8725 from mattdbridges/patch-2

Typo and grammar fixes in the ActionPack CHANGELOG
Rename update_attributes method to update, keep update_attributes as an alias
Change docs to use update instead of update_attributes