* Changed ContentSender demand from iterate()+IDLE to succeeded()+SCHEDULED.
  This ensures that there is no re-iteration in case a 100 Continue response arrives.
  This, in turn, avoids that the demand is performed multiple times, causing ISE to be thrown.
* Changed the 100 Continue action of the proxy Servlet/Handler, that provides the request content, to be executed by the HttpSender, rather than by the HttpReceiver.

Signed-off-by: Simone Bordet <simone.bordet@gmail.com>

* Now `HttpClient` removed the `Expect` header if there is no request content.
* Changed AbstractProxyServlet and ProxyHandler check for request content: now the Content-Type header is not taken into consideration.
* Now the server avoids sending the 100 Continue response if there is no request content.

Signed-off-by: Simone Bordet <simone.bordet@gmail.com>

…continue-fixes'.

Now the request body is not defaulted if missing, but just kept null.

Signed-off-by: Simone Bordet <simone.bordet@gmail.com>

…continue-fixes'.

Signed-off-by: Simone Bordet <simone.bordet@gmail.com>

Signed-off-by: Simone Bordet <simone.bordet@gmail.com>

Signed-off-by: Simone Bordet <simone.bordet@gmail.com>