Reviewer Ellie: Tel URIs part II

Hi Ellie. Please can you review the changes for the remainder of my sprout tel URIs work? This includes the following changes:

* Route failed ENUM lookups to the BGCF rather than rejecting them. This also means doing a default translation when we don't have an ENUM server configured. This includes rejigging the UTs.
* Extracting a list of aliases from the Service Profile and pumping them back through to scscfsproutlet.cpp. This includes hssconnection UTs. This work was needed for the next section.
* Adding a second PAI header when required. This includes full UTs in scscf_test.cpp.

I haven't done any live testing, the UTs are adequate.

Let me know if you have any questions.

Thanks,
Graeme 
This has moved out of the _as_chain_link.is_set check - is this correct?