Add test for malformed Contact expires parameters.
Add test for malformed Contact expires parameters.

From http://tools.ietf.org/html/rfc3261#page-52

   The "expires" parameter of a Contact header field value indicates how
   long the URI is valid.  The value of the parameter is a number
   indicating seconds.  If this parameter is not provided, the value of
   the Expires header field determines how long the URI is valid.
   Malformed values SHOULD be treated as equivalent to 3600.

josephfrazier/sippers,joseph-onsip/sippers