Refactor serialization test for hash order
blorgh_engine to blorgh [ci-skip]
Dont' check for any order in hash since we aren't sorting it and this is determinated only by the used interpreter
Rename @locals to @_locals in Thread to avoid conflict with Rubinius. Closes #11831
Add note about installing and running Memcached for Rails test suite tests that depend on it. [ci skip]
duration is called multiple times in dev, so lets cache it
oops, I missed this in 7193f75
Fix typo [ci skip]
clarify instructions in contributing_to_ruby_on_rails.md for committing [ci skip]
explain how to contribute to the documentation.

Follow-up to #11934
let AR::FinderMethods#exists? return singletons in all cases [closes #11592]

This fixes a regression. The documentation said in its introduction
paragraph that the method returns truthy/falsy, but then below it
was said that if there were no arguments you'd get `true` or `false`.
Also when the argument is exactly `false` a singleton is documented
to be returned.

The method was not returning the singletons so it didn't conform to
those special cases.

The best solution here seems to be to just return singletons in all
cases. This solution is backwards compatible. Also, the contract
has been revised because it has no sense that the predicate varies
that way depending on the input. I bet the previous contract was just
an accident, not something mixed on purpose.

Conflicts:
	activerecord/lib/active_record/relation/finder_methods.rb
	activerecord/test/cases/finder_test.rb
documents 565c367 in the CHANGELOG
Fix the indentation on the from template of the scaffold generator
Creating an SSE class to be used with ActionController::Live.
Normalize file parameters in same place as other parameters (ActionDispatch::Http::Parameters#normalize_encode_params)
Organize normalize_encoding_params' conditionals a bit better and use a case statement for it

Refactor of the work done in #11891
Use each_with_object
ensure freeze on Thread freezes locals
Change the wording to explain following methods skip callbacks [ci skip]
Stop interpreting SQL 'string' columns as :string type.

SQL doesn't have a string type, and interpreting 'string' as text is
contrary to at least SQLite3's behavior:

"Note that a declared type of 'STRING' has an affinity of NUMERIC, not TEXT."
http://www.sqlite.org/datatype3.html