On-demand generation of TicketObject on Ticket and Article ObjectType driver.

Hi,

When DynamicFieldBackendObject is generated, load all registered ObjectType driver.
So if we define thrid ObjectType driver as FAQ and/or Survey, it may cause a infinate loop of recursion
or a cyclic reference.

For example, if we define FAQ ObjectType driver, as below.

1 TicketObject is generated in modules.
2 DynamicFieldBackendObject without pass of FAQObject is generated in TicketObject->new.
3 Ticket and FAQ ObjectType driver is loaded.

4 FAQObject is generated in FAQ ObjectType driver.
5 DynamicFieldBackendObject without pass of TicketObject is generated in FAQObject->new.
6 Ticket and FAQ ObjectType driver is loaded.

7 TicketObject is generated in Ticket ObjectType driver.
8 DynamicFieldBackendObject without pass of FAQObject is generated in TicketObject->new.
........
Falled in infinate loop of recursion.

This PR change generation of TicketObject on Ticket and Article ObjectType driver into on-demand.

Regards,
Norihiro