Rename Model.engine to active_relation_engine. Cache arel_table and the method takes no arguments now

Make Model.all return an array rather than a relation for consistency. Use Model.scoped to get a relation

Add Model.select/group/order/limit/joins/conditions/preload/eager_load class methods returning a lazy relation.

  Examples :

    posts = Post.select('id).order('name') # Returns a lazy relation
    posts.each {|p| puts p.id } # Fires "select id from posts order by name"

Replace reset_counter_cache with reset_counters that has API inline with existing update_counters method

[#1211 state:committed]
Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>

[#1211 state:committed]
Signed-off-by: NJeremy Kemper <jeremy@bitsweat.net>

Revert "Split arel_table into method to get a relation and another to memoize the default relation."

This reverts commit bd517908.

Move validator, human_name and human_attribute_name to ActiveModel, remove deprecated error messages and add i18n_scope and lookup_ancestors.
Signed-off-by: NCarl Lerche <carllerche@mac.com>