remove calls to deprecated find(:first) in actionpack test suite

Tiny refactoring in NumberHelper and RecordTagHelper

- do not use merge! just for 2 values
- there is no need to check block arity

remove unnecessary else statement

Namedspaced generator indent method test refactoring

EXPLAIN only for sqlite3

Fix #5847 and #4045. Load AR::Base before loading an application model.

This feature enables the ability to load an
external routes file from the router via:
  draw :filename

External routes files go in +config/routes+. This
feature works in both engines and applications.

Always quote hstore keys and values

Conflicts:
	activerecord/test/cases/associations/belongs_to_associations_test.rb