[Serdev] ENUM enhancements

[Klaus Darilion]

Hi!

With the current enum resolver, I don't like the fact that I have to 
perform 2 ENUM lookups (=> 2 DNS lookups) for supporting both "E2U+sip" 
and "E2U+voice:sip).

I thought of enhancing the enum lookup function to support multiple 
service types in one function call, separating the service with the + 
sign (the + sign must not occur in the service field), e.g.

   enum_query("e164.arpa.", "sip+voice:sip");

Any comments before I write the patch?

regards,
klaus