[Reviewer: Mike] Add UT for homestead issue 94

Mike,

Please can you review my UT for the https://github.com/Metaswitch/homestead/issues/94 issue?  Bizarrely, the fix is in cpp-common, and the UT is in sprout but this actually fixes a homestead bug.  (In fairness, the bug also exists in sprout - just no-one spotted it.)

Thanks,

Matt