The Template cache in the Resolver can be accessed by multiple threads
similtaneously in multi-threaded environments. The cache is implemented
using a Hash, which isn't threadsafe in all VMs (notably JRuby).

This commit extracts the cache to a new Cache class and adds mutexes to
prevent concurrent access.

Removed old text_helper apis for highlight, excerpt and word_wrap

Fix incorrect assert_block -> assert conversion. Assumed too much from the MiniTest deprecation message.

Reverted changes:
  f3482a9f Fix tests in railties
  5904295b improve #6318
  aed906af prevent using already loaded Gemfile for 'bundle install'

In order to fix this, we need a fix in bundler related to GEM_PATH,
which will allow to run tests properly. I will get this changes back
when it happens.

TagHelper creates invalid data attributes when value is a BigDecimal

Postgresql doesn't accept limits on binary (bytea) columns.

Fix has secure password

Created a Raw handler for templates.

Fixes #2394

Don't allow to destroy readonly models

Fix warning: ambiguous first argument.

Fix documentation around duplicable regarding Class and Module.

AS::Callbacks remove useless code, improve performance

Relation#from to accept other Relation objects

Conflicts:
	activerecord/lib/active_record/core.rb

This reverts commit 8d7c38b8.

Reason: Lot of the additions aren't adding value.

[ci skip]

exercise, fix typos

[getting started] dialog box is not automatic, is provided through jquery_ujs, which is necessary to have in application layout

AS::Callbacks: simplify logical statement