undo bbf2f6b7a5d5f37b2e0c5ef0d31b6ee58442631d
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.
Pass test for malformed Contact expires parameters.

See previous commit.
Add ParsedError. Check request headers, CSeq num.

1. ParsedError is an Error suggesting a status code and reason phrase with
which the application should respond, if the message was a Request. A
ParsedError also contains a parsed message in which malformed headers are left
unparsed.

2. When parsing a Request, ensure that To, From, CSeq, Call-ID, Max-Forwards,
and Via headers are present and well-formed. Throw a ParsedError if they
aren't.  See http://tools.ietf.org/html/rfc3261#section-8.1.1

3. When parsing any SIP message, ensure that the CSeq sequence number is less
than 2**32. Throw a ParsedError if it isn't. See
http://tools.ietf.org/html/rfc3261#section-20.16.