#162 resins tag handler reuse problem

[Robert Schaffar-Taurok]

As stated here:
http://www.caucho.com/resin-3.0/jsp/tutorial/taglib-reuse/index.xtp
, resin reuses tag handlers.

This creates a problem with sorting, because the
attributeMap and headerAttributeMap in
org.displaytag.tags.ColumnTag are not reinitialized for
every usage.

The effect is, that added style classes are kept for
reused tags. This can lead to multiple table header
columns containing the style "order1" for example.

Proposed solution:

do:

attributeMap = new HtmlAttributeMap();
headerAttributeMap = new HtmlAttributeMap();

at the end of the doEndTag() method.

br, Robert