- Use size_t instead of unsigned int for offset.
 - Add function to enable marshal check at runtime.
 - Enable marshal check in unit tests.

 - Use our own implementation of snprintf() called belle_sip_snprintf() to handle the various native implementations whose return values are not consistent.
 - Simplify error handling in marshalling.

* fix many bugs and crashes:
  - rport shall not be set if not present in the request
  - received shall not be set if identical to via's host
  - belle_sip_response_get_return_hop() wasn't working without received parameter
  - belle_sip_response_get_return_hop() wasn't working if no rport and no port (that is default port to be used).

Header name parsing is nno longuer case sensitive

remove qop from default authorization