Exclude the JME package from the build unless the library is detected.

git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@3523 542714f4-19e9-0310-aa3c-eee0fc999fb1

build.xml

@@ -73,6 +73,12 @@
     </apply>
   </target>
 
+  <!-- checks the availability of certain libraries -->
+  <target name="check-available">
+    <available property="jme.present"
+     classname="com.jme.scene.Node" classpathref="classpath"/>
+  </target>
+
   <!-- prepares the application directories -->
   <target name="prepare">
     <mkdir dir="${deploy.dir}"/>
@@ -94,11 +100,12 @@
   </target>
 
   <!-- build the java class files -->
-  <target name="compile" depends="prepare">
+  <target name="compile" depends="check-available,prepare">
     <javac srcdir="src/java" destdir="${classes.dir}"
            debug="on" optimize="{$build.optimize}" deprecation="on"
            source="1.4" target="1.4">
       <classpath refid="classpath"/>
+      <exclude name="com/threerings/jme/**" unless="jme.present"/>
       <exclude name="**/OggPlayer.java"/>
       <exclude name="**/ModPlayer.java"/>
       <exclude name="**/MidiPlayer.java"/>