RUBY-376 use new seed nodes first

lib/mongo/util/pool_manager.rb

@@ -272,7 +272,7 @@ module Mongo
 
     def update_seed_list(members)
       current_members = members.map { |n| n.host_port }
-      @seeds = (@seeds + current_members).uniq
+      @seeds = (current_members + @seeds).uniq
     end
 
   end

test/replica_sets/basic_test.rb

@@ -28,6 +28,7 @@ class BasicTest < Test::Unit::TestCase
       [self.rs.host, self.rs.ports[2]], [self.rs.host, 19356], :name => self.rs.name)
     assert @conn.connected?
     assert @conn.seeds.include?([self.rs.host, 19356]), "Original seed nodes not cached!"
+    assert_equal [self.rs.host, 19356], @conn.seeds.last, "Original seed nodes not cached!"
   end
 
   def test_accessors