Return stale=true if authentication fails because AV not found
Update UTs to check stale parameter
Update stale parameter for digest auth as well
Fix bug breaking live tests
Merge pull request #775 from Metaswitch/issue631

[Reviewer Matt] Set stale=true in WWW-Authenticate header
Merge pull request #776 from Metaswitch/issue436

[Reviewer Andy] Fix bug in Timer C support breaking live tests