ActiveRecord::Relation#blank? should `LIMIT 1`

This is an SQL improvement to ActiveRecord::Relation#blank?. Currently,
it calls `to_a` on the Relation, which loads all records in the
association, and calls `blank?` on the loaded Array. There are other
ways, however, to check the emptiness of an association that are far
more performant. `#empty?`, `#exists?` and `#any?` all attach a `LIMIT
1` to the SQL query before firing it off, which is a nice query
improvement. `#blank?` should do the same!

Bonus performance improvements will also happen for `#present?`, which
merely calls the negation of `#blank?`

Signed-off-by: David Celis <me@davidcel.is>
Merge pull request #10539 from davidcelis/ar-sql-improvements

Improve performance of ActiveRecord::Relation#blank?
Revert "Merge pull request #10539 from davidcelis/ar-sql-improvements"

This reverts commit 257fa6897d9c85da16b7c9fcb4ae3008198d320e, reversing
changes made to 94725b81f5588e4b0f43222c4f142c3135941b4b.

The build failed

https://travis-ci.org/rails/rails/builds/7883546
Update Getting Started Guide - Strong Parameters
	modified:   guides/source/getting_started.md
Merge pull request #10872 from AJAlabs/master

Update Getting Started Guide - Strong Parameter [ci skip]
’ -> ' [ci skip]
Override Time.at to work with Time-like values

Time.at allows passing a single Time argument which is then converted
to an integer. The conversion code since 1.9.3r429 explicitly checks
for an instance of Time so we need to override it to allow DateTime
and ActiveSupport::TimeWithZone values.
fixed typo in action_view template
Getting rid of the +automatic_inverse_of: false+ option in associations in favor
of using +inverse_of: false+ option. Changing the documentation and
adding a CHANGELOG entry for the automatic inverse detection feature.
Testing CheckPending middleware
Merge pull request #10893 from arunagw/test_for_checkpending_middleware

Testing CheckPending middleware
Merge pull request #10889 from diatmpravin/fix-typo-in-action-view

fixed typo in action_view template
Fixed typos in activesupport [ci skip]

- eval'ed to eval'd in accordance with https://github.com/rails/rails/pull/10889
- tried to improve statement about compiling Procs into methods using define_method
Merge pull request #10886 from wangjohn/chnges_for_automatic_inverse_associations

Documentation and cleanup of automatic discovery of inverse associations
cleanup whitespace in relation.rb
Remove fall back and column restrictions for `count`.
Merge pull request #10710 from senny/5554_let_the_database_raise_on_counts

Remove column restrictions for `#count`, let the database raise if the SQL is invalid.
Don't blindly call blame_file! on exceptions in ActiveSupport::Dependencies::Loadable

It is possible under some environments to receive an Exception that is
not extended with Blamable (e.g. JRuby).
ActiveSupport::Dependencies::Loadable#load_dependency blindly call
blame_file! on the exception which throws it's own NoMethodError
exception and hides the original Exception.

This commit fixes #9521
Merge pull request #10795 from atambo/master

Don't blindly call blame_file! on exceptions in ActiveSupport::Dependes::Loadable
fix ActiveModel::Validations.validators_on doc