[Serdev] ENUM enhancements

[Juha Heinanen]

Klaus Darilion writes:

 > I think every string comparison is negligible compared to a second DNS 
 > lookup.

that is true, but i don't want to take any performance penalty for those
who use the simple, ietf recommended service field e2u+sip.  also, in
order to make debugging of the code simple, the extra logic that is
needed for more complicated options should be separate from the simple
case, not mixed up in it.

-- juha