Drop qt devices if ENABLE_qt (which activates the build of the plplotqtd library which the qt devices depend on) is false.
Drop qt devices if ENABLE_qt (which activates the build of the plplotqtd
library which the qt devices depend on) is false.

svn path=/trunk/; revision=12630

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