Negotiate: fix for HTTP POST with Negotiate

* Adjusted unit tests 2056, 2057
* do not generally close connections with CURLAUTH_NEGOTIATE after every request
* moved negotiatedata from UrlState to connectdata
* Added stream rewind logic for CURLAUTH_NEGOTIATE
* introduced negotiatedata::GSS_AUTHDONE and negotiatedata::GSS_AUTHSUCC
* Consider authproblem state for CURLAUTH_NEGOTIATE
* Consider reuse_forbid for CURLAUTH_NEGOTIATE
* moved and adjusted negotiate authentication state handling from
  output_auth_headers into Curl_output_negotiate
* Curl_output_negotiate: ensure auth done is always set
* Curl_output_negotiate: Set auth done also if result code is
  GSS_S_CONTINUE_NEEDED/SEC_I_CONTINUE_NEEDED as this result code may
  also indicate the last challenge request (only works with disabled
  Expect: 100-continue and CURLOPT_KEEP_SENDING_ON_ERROR -> 1)
* Consider "Persistent-Auth" header, detect if not present;
  Reset/Cleanup negotiate after authentication if no persistent
  authentication
* apply changes introduced with #2546 for negotiate rewind logic

Fixes #1261
Closes #1975