Plugin should check if Manul Proxy setting is empty

Plugin always sets a RMISocketFactory in case of using a proxy, even when control panel has "Use browser proxy" unchecked and all the proxy fields left empty.

For intranet RMI applet and server, the applet might also need to use SSL enabled socket to protect sensitive data. In order to do that, user's applet code has to set a SSLRMISocketFactory. This will fails since plugin already has set a RMISocketFactory. The only way to make it work is that user has to unset the proxy server on the browser -- a big inconvenience.