Make tooltips on Expressions and Sequences only visible if the filename is longer than the list width

[GoogleCodeExporter]

EB currently doesn't have tooltips, but SB does.  Add them to EB, but in both 
cases only make them appear if the file name is too long to fit in the width of 
the list.

Original issue reported on code.google.com by garthabr...@gmail.com on 24 Oct 2011 at 9:01