Setting own comparator for column sorting

====
imported from sf tracker
id 1020990
submitted by Diego Werba Montiel - dwerbam
http://sourceforge.net/tracker/index.php?func=detail&group_id=73068&atid=536613&aid=1020990
====

I made some changes to rc1 to solve the problem for
sorting (how to compare row values).

Adding a "comparator" attribute to display:column you
can specify the full classname that will solve how to
order the rows.

I don't know if it is the "best" way to resolve the
problem but it works.

You can check the solution in the attached patch file or
even rewrite rc1 sources with it and execute maven.

Seeya