[Paraview] Not a valid QT plugin on windows

[Utkarsh Ayachit]

>> As a side note, I attempted to set the environment variable
>> PV_PLUGIN_DEBUG as described at
>> http://paraview.org/Wiki/Plugin_HowTo#Debugging_Plugins in order to obtain
>> more information, but it didn't seem to have any effect.  There was no
>> additional output in either the Output Messages window or the terminal from
>> which paraview was started.

The PV_PLUGIN_DEBUG variable was added recently in CVS and will be
available with 3.8. It won't work with 3.6.*

Utkarsh