BasicServiceImpl.showDocument() needs to be overridden in JNLP support for new plug-in

In the new support for launching applets from JNLP files in the new Java Plug-In, the Java Plug-In reuses the implementations of several JNLP services like the BasicServiceImpl. Unfortunately, the BasicServiceImpl's showDocument() support is over-specialized for Java Web Start. There are two problems with it: first, it re-initializes the DesktopBrowse class, which is not allowed, and second, showDocument() is implemented by launching a new process instead of sending a message back to the web browser via the new plug-in's existing showDocument() support.

The BasicServiceImpl code needs to be changed and/or refactored to allow overriding of its showDocument() implementation, which is not currently possible. Additionally, the JNLP2Manager needs to be changed to override it by sending a message back to the browser, likely with a _target of "blank" to create a new window to avoid destroying the applet during the showDocument() call (which is unlikely to be the desired behavior).