Add support for user-defined MIME headers in TIdMultipartFormDataStream

[rlebeau]

Add a headers property to TIdFormDataField (similar to TIdMessage.CustomHeaders and TIdMessagePart.Headers) so users can customize the MIME headers. For example, some servers may support a Content-MD5 header when uploading files.

[icegood]

rlebeau, tnx. You created it as a result of our convesation. But there is a workaround for now. It works fine for me:

AmyHTTP.Request.CustomHeaders.Add('Expect: 100-continue');
AmyHTTP.Request.CustomHeaders.Add(Format('Content-MD5: %s', [AMD5Header]));
AmyHTTP.Post(AUrl, AMultiPartFormData);

as it seems that AMultiPartFormData headers just added to headers of request and merged with AmyHTTP.Request.CustomHeaders.

[rlebeau]

That applies the Content-MD5 header to the entire HTTP request body as a whole, not to any specific MIME field. When sending MIME data, the Content-MD5 header should be applied to the particular MIME field(s) that are actually being hashed.