Please add the checkhelpsets task to the objectbrowser build.xml file. For 
reference, below is part of the code that appears in usersguide's build file. 
This task enables me to check html and xml links in the help set when I call 
the build script with the "check-javahelp" option.

  <!-- See #13931: -->
  <target name="check-javahelp" depends="javahelp" description="Validate 
helpset for various errors.">
    <taskdef name="checkhelpsets" 
classname="org.netbeans.nbbuild.CheckHelpSets" 
classpath="../nbbuild/nbantext.jar:${binroot}/core/release/lib/ext/regexp.jar:${
binroot}/nbbuild/lib/jhall.jar"/>
    <checkhelpsets>
      <fileset dir="javahelp">
        <include name="org/netbeans/modules/usersguide/ide.hs"/>
      </fileset>
    </checkhelpsets>
  </target>