Overridable property "fo.examples.include" added to select which examples to build

git-svn-id: https://svn.apache.org/repos/asf/xmlgraphics/fop/trunk@448523 13f79535-47bb-0310-9956-ffa450edef68

build.xml

   <property name="src.viewer.images.dir" value="${src.java.dir}/org/apache/fop/render/awt/viewer/images"/>
   <property name="xdocs.dir" value="${src.dir}/documentation/content/xdocs"/>
   <property name="fo.examples.dir" value="${basedir}/examples/fo/basic"/>
+  <property name="fo.examples.include" value="**/*.fo"/>
   <property name="lib.dir" value="${basedir}/lib"/>
   <property name="user.hyph.dir" value="${basedir}/hyph"/>
 
     <fop format="${build.property.examples.mime.type}" outdir="${build.examples.dir}"
          messagelevel="debug" basedir="${fo.examples.dir}">
       <fileset dir="${fo.examples.dir}">
-        <include name="**/*.fo"/>
+        <include name="${fo.examples.include}"/>
       </fileset>
     </fop>
   </target>