Reset the global flags that say we have a MANIFEST.MF/web.xml after
execute has been run.
<jar> would print a warning in Ant's own bootstrap when it zipped
ant.jar for the second time.
git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@268398 13f79535-47bb-0310-9956-ffa450edef68