Andrew Biggs pointed out a "Expect: 100-continue" flaw where libcurl didn't

send the whole request at once, even though the Expect: header was disabled
by the application. An effect of this change is also that small (< 1024
bytes) POSTs are now always sent without Expect: header since we deem it
more costly to bother about that than the risk that we send the data in
vain.

tests/data/test510

@@ -39,7 +39,6 @@ Host: 127.0.0.1:%HTTPPORT
 Accept: */*
 Transfer-Encoding: chunked
 Content-Type: application/x-www-form-urlencoded
-Expect: 100-continue
 
 3
 one