Tweak CMake logic so that PC_REQUIRES_TAG is set locally in all cases rather than relying on the existing default value of PC_REQUIRES_TAG which may disappear in the future.
Tweak CMake logic so that PC_REQUIRES_TAG is set locally in all cases
rather than relying on the existing default value of PC_REQUIRES_TAG
which may disappear in the future.


svn path=/trunk/; revision=12034

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