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)
Digestor explicit dependency should not contain trailing whitespace

test for rails/rails#8586
Merge pull request #8586 from balexand/cache_digests_regex

Digestor explicit dependency should not contain trailing whitespace
return Mime::NullType if format is unknown

If a request has an unknown format, the methods html?, xml?, json? ...etc
not raise an Exception.

This patch add a class Mime::NullType, that is returned when  request.format is unknown
and it responds false to the methods that ends with '?' and true to 'nil?'.

It refers to #7837, this issue is considered a improvement not a bug.
Merge pull request #8085 from acapilleri/format_never_nil

if format is unknown NullMimeTypeObject is returned
Install binstubs by default
Detect rbenv and update the shebang
Add --no-html to scaffold generator
Forgot to check in railties fixture for binstubs
Ignore /bin on new apps
adds kindlerb to the :doc bundle group for guides generation
Fixes for PR [#8267]
* Fix Migration#reversible by not using `transaction`.

* Adapt mysql adapter to updated api for remove_column

* Update test after aedcd683684d08eaf30623a4b48ce31a31426372
Fix syntax error in controller template
Fix spacing regression in scaffold generator
Merge pull request #8588 from marcandre/fix_reversible

Fix Migration#reversible by not using `transaction`.
Remove warning of intance variable not initialized
remove duplication from Rails::Application docs
Merge pull request #8593 from shime/master

another little documentation fix