Addition of Oidxs and Oids.

[Jochen Katz]

Hi,

>        Is there any reason why the addition operator is missing from Oid 
> and Agentpp::Oidx classes ?

perhaps because the original author thought that every Oid starts with 
1.3 and so it does not make sense to add one oid to another. I added the 
function for the next release.

Regards,
   Jochen