has_many associations with :dependent => :delete_all should update the counter cache when deleting records

Fix problem where wrong keys are used in JoinAssociation when an association goes :through a belongs_to [#2801 state:resolved]

Remove unnecessary overloaded methods create, create! and create_record from HasAndBelongsToManyAssociation

Delete create, create! and create_record from HasManyThroughAssociation in exchange for more generic versions in AssociationCollection

Specify insert_record with NotImplementedError in AssociationCollection, to indicate that subclasses should implement it. Also add save_record to reduce duplication.

Signed-off-by: NJosé Valim <jose.valim@gmail.com>

Signed-off-by: NJosé Valim <jose.valim@gmail.com>

Based on the implementation on the 2-3-stable branch, patches by Hongli
Lai <hongli@phusion.nl>, and helpful suggestions from José Valim.

Hongli Lai's patches included locking around the request cycle; this is
now handled by Rack::Lock (https://github.com/rack/rack/issues/issue/87/).

[#2873]
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

Remove weak_passwords list and the length/strong password validator, leave that up to the programmer