Implement -portrait option with plsportrait.  Use public API plsfreeaspect to implement -freeaspect option. Some commentary/documentation changed.
Implement -portrait option with plsportrait.  Use public API plsfreeaspect
to implement -freeaspect option. Some commentary/documentation changed.

svn path=/trunk/; revision=3127

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