Link color brushing
Link glyph brushing
Link erase brushing

When one of these is on, then two or more XGobis that were
initiated with the same data (or have the same number of rows)
*or* have the same value of `fname.nlinkable' are linked for
point 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.

If <any> of these is on, 'delete erased,' found on the erase menu
in the Brush mode, is also linked.

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

These variables can be set in the XGobi resource file.  The defaults
are:

*linkGlyphBrush: True
*linkColorBrush: True
*linkEraseBrush: True
