I couldn’t install JBoss GWT Integration from http://download.jboss.org/jbosstools/updates/nightly/trunk/ because I was getting an error like
Cannot complete the install because one or more required items could not be found.
Software being installed: JBoss GWT Integration (Experimental)
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I solved my problem downloading JBoss GWT Integration from:
http://download.jboss.org/jbosstools/updates/development/indigo/