Fix#3566
Also update testsuite so that all tests read and write some data. Opening a connection is not enough to trigger connection errors, because the connection is so lazy.
* Add H2C support to server
* update comment
* Make http1.1 ALPN work on SplitHTTP client
Users that encounter protocol version issues will likely try to set the
ALPN explicitly. In that case we should simply grant their wish, because
the intent is obvious.
hellokindle