build fix, use lambda syntax that ruby 1.9.3 understands.
Revert "Merge pull request #14544 from jefflai2/named_scope_sti"

This reverts commit eed1e2568261172d99e9f3607cb379424f14f5b3.

Conflicts:
	activerecord/CHANGELOG.md
	activerecord/test/models/comment.rb

This change break integration with activerecord-deprecated_finders so
I'm reverting until we find a way to make it work with this gem.
Add has_and_belongs_to_many back to reflections hash.

This adds back `has_and_belongs_to_many` reflection to the reflections
hash. Even thought we are not using that internally, as
`Model.reflections` is a public method we need to keep the hash of
reflections coherent.

ad7b5efb55bcc2e0ccd3e7f22a81e984df8676d1 is the commit that made
has_and_belongs_to_many became a has_many :through and a has_many.

[fixes #14682]
Small test syntax change
Replace reflect_on_all_associations internally
Add _reflect_on_association method for internal use

Internally we wanna look-up the reflection by the association name in
the private list of reflections, so I am adding a
_reflect_on_association method that does that.