[patch] Ensure necessary included tables are joined in construct_finder_sql_for_association_limiting

Currently selecting limited ids for eager loading associations is broken when there is a condition or an order-by based on a table that is not directly joined to the main active record table.

so if I have:

class Person
  has_many :items
end

class Item
  belongs_to :person
  has_one :another_item
end

class AnotherItem
  belongs_to :item
end

Person.find(:all, 
            :include=>{:items=>:another_item}, 
            :order=>" another_items.name ASC ",
            :limit=>4)

The find will fail because the join to table items will not be included.

The patch adds methods to the join_dependency to look up joins by aliased table name, and get an array of the joins required to reach that table.