Fix a sign problem with subscripts that was causing them to become superscripts.
Fix a sign problem with subscripts that was causing them to become superscripts.

svn path=/trunk/; revision=8857

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