New authentication code added, particularly noticable when doing POST or PUT

with Digest or NTLM. libcurl will now use HEAD to negotiate the authentication
and when done perform the requested POST.

tests/data/test88

@@ -62,12 +62,10 @@ four is the number of lines
 ^User-Agent:.*
 </strip>
 <protocol>
-PUT /88 HTTP/1.1
+HEAD /88 HTTP/1.1
 Host: 127.0.0.1:8999
 Pragma: no-cache
 Accept: */*
-Content-Length: 85
-Expect: 100-continue
 
 PUT /88 HTTP/1.1
 Authorization: Digest username="testuser", realm="testrealm", nonce="1053604145", uri="/88", response="78a49fa53d0c228778297687d4168e71"