Miscellaneous cleaning up, comments added.  Functions added for converting from device coordinates to other coordinates.
Miscellaneous cleaning up, comments added.  Functions added for converting
from device coordinates to other coordinates.

svn path=/trunk/; revision=1504

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