Cleaner queuing of jobs using Delayed Job
Update error message for validate method

- Improve the error message by suggesting that the user may have
  intended to call validates instead of validate method.
Merge pull request #16851 from prathamesh-sonpatki/mention-validate-in-upgrade-guide

Update error message of Active Model's validate method
Move the array to a constant
Revert "Merge pull request #16888 from jejacks0n/render_template"

This reverts commit 07635a74b5ee08dcba3f6617def6230d8f114fe5, reversing
changes made to 1b5f61a025b6ce1ee52b7148e3ed2a9acbde28b9.

Reason: it's not ready :bomb:, see https://github.com/rails/rails/pull/16888#issuecomment-56400816
fix fixtures not loading if a belongs_to association is defined with a :foreign_key option that's a symbol
Better regression test for Fixtures with fk as a symbol
Merge pull request #17009 from arthurnn/foreign_key_symbols

Fixtures using Foreign key symbols
Merge pull request #16963 from collectiveidea/activejob-dj

Cleaner queuing of jobs using Delayed Job

Conflicts:
	activejob/lib/active_job/queue_adapters/delayed_job_adapter.rb
Clarify the documentation of the primary_key option for associations

Previously the documentation stated that `primary_key` should be the name of
a *method* that returns the primary key used for the association. This is
incorrect. This changes the documentation to say that the value must be the
name of a column.
Merge pull request #17012 from petedmarsh/clarify-association-primary-key-option-documentation

Clarify the documentation of the primary_key option for associations
add a truncate method to the connection

it doesn't work on SQLite3 since it doesn't support truncate, but that's
OK.  If you call truncate on the connection, you're now bound to that
database (same as if you use hstore or any other db specific feature).