remote-curl: fall back to basic auth if Negotiate fails

remote-curl: fall back to basic auth if Negotiate fails

When the username and password are supplied in a url like this
https://myuser:secret@git.exampe/myrepo.git and the server supports the
negotiate authenticaten method, git does not fall back to basic auth and
libcurl hardly tries to authenticate with the negotiate method.

Stop using the Negotiate authentication method after the first failure
because if it fails on the first try it will never succeed.

Signed-off-by: Christopher Schenk <christopher@cschenk.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>