Define qt_gui_true to be used in the installed examples/c++ Makefile.
Define qt_gui_true to be used in the installed examples/c++ Makefile.

svn path=/trunk/; revision=9816

FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot