Bug#513881: reason for crash

[Josh Metzler <joshdeb@metzlers.org>]

I've been looking at konqueror-nsplugins, and I think I see why it is crashing 
with gtk-qt-engine installed.  Basically, nspluginviewer is a qt4 application 
that loads plugins, including some that are gtk based (such as flashplugin-
nonfree).  When such a gtk using plugin is loaded and gtk-qt-engine is in use, 
both qt3 and qt4 are loaded.  It is similar to the situation mentioned here:

http://labs.trolltech.com/forums/topic/414

Where Trolltech said it would not work with default builds of qt3 and qt4.  So 
I think the Conflicts is appropriate to add.

Josh