Specify the amount of memory for OOXMLLite as different environments fail sometimes currently and it should make the build more reproducible if we state how much memeory we want

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1697233 13f79535-47bb-0310-9956-ffa450edef68

build.xml

@@ -1197,6 +1197,7 @@ under the License.
             <classpath refid="ooxml.xmlsec.classpath"/>
             <syspropertyset refid="junit.properties"/>
             <jvmarg value="-XX:MaxPermSize=256m"/>
+            <jvmarg value="-Xmx512m"/>
             <arg value="-ooxml"/>
             <arg value="${ooxml.lite-merged.dir}/ooxml-lite-merged.jar"/>
             <arg value="-test"/>