Read P-Served-User to determine served user.

(if available).

PJUtils now has a method to parse a URI-containing header. This
parsing requires a pool, so thread that through.

Tidy up some out-of-date comments.
Basic P-Asserted-Identity support on ISC i/f.
Pass reg-state info to AsChain.
Add support for sending P-Served-User.
Common code to set a generic header.
Tidy up: parse AS URI in IfcHandler (placeholder).

Only a placeholder for now, due to imminent merge.
Remove workaround for demo AS.

The demo AS can't talk to bono (because it can't talk TCP), so
Sprout previously did a record-route on either side. This removes that.
Remove broken UT.

We no longer parse the URI in aschain, so it doesn't make sense
to test it there.
Set Req-Disp: no-fork when invoking non-final ASs.
Full UT coverage of P-S-U changes. Bugfix.

P-S-U parsing wasn't correctly picking up the end of the URI
in name-addr format.
Add missing test for full coverage.

Test invalid P-Served-User header.
Merge branch 'dev' of github.com:Metaswitch/sprout into isc-headers

Conflicts:
	include/aschain.h
	sprout/aschain.cpp
	sprout/ifchandler.cpp
	sprout/stateful_proxy.cpp
	sprout/ut/aschain_test.cpp
Code review markup.
Merge pull request #8 from Metaswitch/isc-headers

[Reviewer: Mike] ISC headers