Function plToGdAlpha is only defined if GD2_VERS >=2 since gdAlphaMax is only available from this version on.
Function plToGdAlpha is only defined if GD2_VERS >=2 since gdAlphaMax is only available from this version on.

svn path=/trunk/; revision=9076

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