Description:
------------
We have observed some new and unexpected behaviour with PUT requests since upgrading from 2.2 to 2.4.1. A PUT request which triggers a HTTP/1.1 100 Continue followed by a 200 OK returns 100 when getResponseCode() is called.

I have supplied a fairly terrible server script below that returns exactly the same response structure as the server we're interacting with which is causing the problem for us.

The request headers I see using both 2.2 and 2.4.1 are the same (apart from the version number in the UA, of course):

PUT / HTTP/1.1
User-Agent: PECL_HTTP/2.4.1 PHP/5.6.7 libcurl/7.37.1
Host: localhost:8081
Accept: */*
Content-Length: 3
Expect: 100-continue

Using 2.2, the client script below shows a response code of 200. Using 2.4.1, it shows 100.

Test script:
---------------
if ($argv[1] == 'server') {
    $s = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
    socket_set_option($s, SOL_SOCKET, SO_REUSEADDR, 1);
    socket_bind($s, "127.0.0.1", 8081);
    socket_listen($s);
    while (true) {
        $c = socket_accept($s);
        $h = socket_read($c, 8192);
        echo $h;
        socket_write($c, "HTTP/1.1 100 Continue\r\n\r\n");
        socket_write($c, implode("\r\n", [
            "HTTP/1.1 200 OK",
            "Content-Length: 3",
            "Content-Type: text/plain",
            "",
            "foo",
            "",
        ])."\r\n");
        socket_close($c);
    }
    socket_close($s);
}
elseif ($argv[1] == 'client') {
    $rq = new \Http\Client\Request('PUT', 'http://localhost:8081/', [], 
        (new \Http\Message\Body)->append("foo")
    );
    $c = new \Http\Client;
    $rs = $c->enqueue($rq)->send()->getResponse();
    var_dump($rs->getResponseCode());
}