[ENH] Lines In Hierarchy ( [et] tested in 5707, visually appealing enhancement for base )

[cdshaffer at acm.org]

Works fine with new SM package browser, StarBrowser, Whisker Browser and
they all looked and worked fine.  I've been using it for several hours
of heavy use of these tools...no problems.  The
EToyHierarchicalTextMorph does not benifit much from these lines (and
looks a little strange when items are collapsed since the subtree arrows
and items disappear when an item is collapsed but the faint lines do
not) but I'm not aware of any extensive use of this morph and one could
always disable this option.

This enhancement looks visually appealing and the fact that it is
controlled by a preference option makes it a good candidate for
integration into base.