Turn off desktop integration for JNLP-launched applets

###@###.### has indicated that occasionally the fact that the new plug-in does the "desktop integration" operation for JNLP-launched applets causes the system to get into such a state that the new plug-in will fail to launch an JNLP-based applet until the desktop integration "program" is removed using the Add/Remove Programs Control Panel.

A separate bug will be filed about the persistent failure to launch when the system gets into this state, because it might indicate a deeper problem that could affect Java Web Start. However, it is essential that we turn off the desktop integration support for JNLP-launched applets, because it doesn't make sense anyway. Double-clicking such a desktop icon to launch the associated JNLP file is meaningless without the surrounding web page.