#6 validator fragment for X-men.

[Akihiro MATOBA]

add xml validation functionality for X-men xml editor and
context menu.

based on a article by muimi (in javavedeloper.jp),
http://www.javadeveloper.jp/members/regular/Rensai.cat
egory_rensai_article_plugin_issue_10.dhtml, and
integrated caching mechanism in x-men by me.

because I use the crimson library instead of xerces, we
can use this in Eclipse 3.0, but cannot use in JDK 1.5.0.

[Akihiro MATOBA]