Dispose web client when connection is lost.

When the server connection is lost in the HTTP proxy, the web client wouldn't be disposed so the website wouldn't know there was a connection loss. Also changed the error message to something a little bit more user friendly.
Created version 1.13.0.0.
Enlarged the header from three to four bytes to accommodate messages of more than 2 MB. Maximum is now 512 MB.
Created version 1.14.0.0.