This macro stretches a line.  There is the option to stretch it until
 it meets another element (line, circle or arc).  It will be extended
 or shrunk to the intersection of the line with the other element,
 even if the line does not actually touch the other element.  For
 example, if the other element is a line, it is considered infinite so
 the line to be streched will be stretched to the point where the two
 lines would intersect.  This is true for circles and arcs as well.
 In those cases, the macro will pick the intersection point closest to
 the point picked on the circle or arc.

Or, the line can be stretched an arbitrary distance by picking a
 point.  In either case the slope of the line is maintained and there
 is graphical feedback about the size of the line as the cursor is
 moved.

The end of the line that is closest to the point picked on the line
will be the one the is changed, the other end will be fixed.

Limitations:

*This only works with lines.

*The line cannot be stretched to a spline.

*The original line is deleted. Only the color and linetype are applied to
 the newly created line; linesize, pensize and INFO attributes are lost.