call tar directly when making osx bundle

When using ant's tar option, the permissions on JavaStubApplication were
getting reset, causing the extracted archive to not be executable. By using the
system's tar the permissions are not reset.

build.xml

@@ -170,7 +170,15 @@
 	    <ant target="dotarbundle" />
     </target>
     <target name="dotarbundle" unless="notarbundle">
-	    <tar destfile="itoopie.app.tar.bz2" basedir="${temp}" compression="bzip2" />
+        <exec executable="tar" osfamily="unix" failonerror="true">
+                <arg value="--owner=root" />
+                <arg value="--group=root" />
+                <arg value="-cjvf" />
+                <arg value="itoopie.app.tar.bz2" />
+		<arg value="-C" />
+                <arg value="${temp}" />
+		<arg value="itoopie.app" />
+	</exec>
     </target>
 
 </project>