Implemented graphic crosshairs, which are turned on or off using the "-xhairs <boolean>" widget configure command.  This inserts an event handler to draw and update the graphic crosshairs on cursor motion, as well as intercepting cursor key movements and moving the drawn cursor appropriately. The expose event handling was broken off into a separate handler and changed to redraw the graphic crosshairs if necessary.
Implemented graphic crosshairs, which are turned on or off using the
"-xhairs <boolean>" widget configure command.  This inserts an event handler
to draw and update the graphic crosshairs on cursor motion, as well as
intercepting cursor key movements and moving the drawn cursor appropriately.
The expose event handling was broken off into a separate handler and changed
to redraw the graphic crosshairs if necessary.

svn path=/trunk/; revision=1484

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