Set -Djava.awt.headless=true for ant test

Makes running tests less annoying with OS X/Java7

build.xml

@@ -1048,6 +1048,7 @@
         <jvmarg value="-Dstorage-config=${test.conf}"/>
         <jvmarg value="-Daccess.properties=${test.conf}/access.properties"/>
         <jvmarg value="-Dlog4j.configuration=log4j-junit.properties" />
+        <jvmarg value="-Djava.awt.headless=true"/>
         <jvmarg value="-javaagent:${basedir}/lib/jamm-0.2.5.jar" />
         <jvmarg value="-ea"/>
         <optjvmargs/>