Return self from #distinct so it's chainable

lib/arel/select_manager.rb

@@ -151,6 +151,7 @@ module Arel
       else
         @ctx.set_quantifier = nil
       end
+      self
     end
 
     def order *expr

test/test_select_manager.rb

@@ -1073,6 +1073,12 @@ module Arel
         manager.distinct(false)
         manager.ast.cores.last.set_quantifier.must_equal nil
       end
+
+      it "chains" do
+        manager = Arel::SelectManager.new Table.engine
+        manager.distinct.must_equal manager
+        manager.distinct(false).must_equal manager
+      end
     end
   end
 end