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
change spy of  after invoked controller action. because ruby-2.0.0 waned unused variables
Eager loading made to use relation's in_clause_length instead of host's one (fixes #8474)
Test nested fields with AssociationProxy mockup & fix AssociationProxy support in form helper
Fix up/down column change example code formatting
Merge pull request #8650 from codeodor/patch-1

Fix up/down column change example code formatting
Document JoinTable migration generator
Update documentation for yml usage
Update documentation for yml usage

Update documentation for yml usage against https://github.com/rails/rails/issues/8612
Rails 4.0 is going to depend on Rack 1.5.x so let's test against Rack master
Merge pull request #8647 from nishantmodak/patch-2

Update documentation for yml usage
warning removed: shadowing outer local variable
Merge pull request #8656 from arunagw/warning_removed_shadowing_var

warning removed: shadowing outer local variable
Update guides/source/layouts_and_rendering.md

Removed first slash. The subdirectory will nto be found with slash befor it.

Fix missing ending newline in db structure dump:

  When dumping database structure with `rake db:structure:dump` and
using migrations, the resulting file will not end with a newline char.
Although it's not mandatory, it breaks a lot of simple use cases with
programs like cat, more, grep, etc.

  This changes use `puts' instead of `<<' to append migration versions
data to the dump and also split the line where this is happening as it
was a bit long.
Improve secret_token deprecation message
Merge pull request #8651 from tjouan/activerecord-structure_dump-ending_nl

Fix missing ending newline in db structure dump:
Point to guides.rubyonrails.org instead of edgeguides.rubyonrails.org
Revert "Rails 4.0 is going to depend on Rack 1.5.x so let's test against Rack master"

This reverts commit fba97c9620e709f0449ea9f3240b9e5174f72e1e.
fixed inconsistent `require 'test_helper'` in testing guide