Loads more UTs, plus bugfix and notes.

UTs to cover all AS flows.

Bugfix for MMTEL call services in cases where there is no body on the
INVITE - we don't want to crash!

MMTEL flows don't all work yet; failing tests are disabled and
comments inserted in code where we need to make a fix.
Merge branch 'dev' of github.com:Metaswitch/sprout into isc-ut-beefup
Reject bad ;orig, and set it correctly ourselves.

;orig can only be set by a known client; other instances are
illegal.

When we set it ourselves, only do it when we are doing it on
behalf of a known client.
UTs, proper trust boundary handling, and comments.

More detailed comments about IBCF ;orig.
Make priority field in iFC optional
Apply review markups.

Clearer to look up the topmost route header again, rather than
relying on a fragile assignment to a local variable a long way
above.
Merge pull request #23 from Metaswitch/isc-ut-beefup

[Reviewer: Mike] ISC UT beefup

Code changes look fine.  I haven't reviewed all the UT test cases - I think that would be redundant in our processes.
Re-enable NoPriority test case (now succeeds)
Fix bad merge - VG guard on wrong test!
Suppress VG errors.

I don't fully understand why we can't get a destroy invocation here,
but I think it's because the transaction isn't actually destroyed
until after a long timer has fired, and we don't wait for that to
happen. For now, just add a suppression.
Merge pull request #28 from Metaswitch/valgrind-fixes

[Reviewer: Mike] Valgrind fixes
Merge pull request #27 from Metaswitch/ifc-priority-optional

Ifc priority optional
Merge pull request #24 from Metaswitch/ibcf-orig

[Reviewer: Mike] IBCF ;orig handling