Use the cluster domain if:

 * We're not an IBCF (and thus a trusted peer downstream)
 * We're not performing outbound (and thus have to be in the call path)
Correctly populate the 'orig'parameter
Remove dodgy test
Use domain name as service route
Better comments
Refactor target to Target and target_list to TargetList
Merge remote-tracking branch 'origin/master' into further-proxying-support

Conflicts:
	include/stateful_proxy.h
	sprout/stateful_proxy.cpp
Fix up UTs
Merge pull request #242 from Metaswitch/further-proxying-support

Reviewer Mike - Further proxying support