Encoding declaration of POSTed XML documents is ignored

Currently, the post.sh script and the SimplePostTool use this header to define encoding:

Content-type:text/xml; charset=utf-8

And the XML encoding declaration of the POSTed document is ignored.

According to RFC 3023, the correct way would be to use "Content-type:application/xml" and use the XML document's encoding.

One this is fixed, the "please use UTF-8 encoding" warning is SimplePostTool can be removed.