Delegate alias_tracker creation to AR Relation rather than doing it o…

…urselves. Closes #1491.

lib/ransack/adapters/active_record/context.rb

@@ -110,7 +110,7 @@ def klassify(obj)
         #
         def join_sources
           base, joins = begin
-            alias_tracker = ::ActiveRecord::Associations::AliasTracker.create(self.klass.connection, @object.table.name, [])
+            alias_tracker = @object.alias_tracker
             constraints   = @join_dependency.join_constraints(@object.joins_values, alias_tracker, @object.references_values)
 
             [
@@ -278,7 +278,7 @@ def build_joins(relation)
 
           join_list = join_nodes + convert_join_strings_to_ast(relation.table, string_joins)
 
-          alias_tracker = ::ActiveRecord::Associations::AliasTracker.create(self.klass.connection, relation.table.name, join_list)
+          alias_tracker = relation.alias_tracker(join_list)
           join_dependency = Polyamorous::JoinDependency.new(relation.klass, relation.table, association_joins, Arel::Nodes::OuterJoin)
           join_dependency.instance_variable_set(:@alias_tracker, alias_tracker)
           join_nodes.each do |join|