AR Associations: Don't clobber :extend options with a block

Right now, blocks passed to an association macro clobber the :extend options. This patch merges the :extend options and block instead.

has_many :projects, :extend => SomeAssociationExtension do   def find_least_recent     find(:first, :order => "id ASC")   end end

http://dev.rubyonrails.org/ticket/9346