100-Continue when POSTing

[wvdvegt]

The A2 System does not support 100-Continue which seems default for .Net HttpWebRequest calls.

HttpWebRequest.Expect100Continue Property: when this property is set to true, client requests that use the POST method expect to receive a 100-Continue response from the server to indicate that the client should send the data to be posted. This mechanism allows clients to avoid sending large amounts of data over the network when the server, based on the request headers, intends to reject the request.

See https://en.wikipedia.org/wiki/List_of_HTTP_status_codes#1xx_Informational
and https://msdn.microsoft.com/en-us/library/system.net.servicepoint.expect100continue(v=vs.110).aspx