Link brushing

When this is on, then two or more XGobis that were initiated
with the same data (or have the same number of rows) are
linked for brushing.  That is, brushing actions performed
in one of the XGobis is promptly reflected in the others.

This is most frequently used when the XGobi plotting windows
display different views of the same data.

Note:  For computational efficiency, the receiving XGobis
should be in XYPlot, DotPlot, or paused in Rotate or Tour.

This can be set in the XGobi resource file.  The default is

*linkBrush:   True
