added assertions as an explicit datatype

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@275275 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/types/defaults.properties

@@ -19,3 +19,4 @@ selector=org.apache.tools.ant.types.selectors.SelectSelector
 zipfileset=org.apache.tools.ant.types.ZipFileSet
 scriptfilter=org.apache.tools.ant.types.optional.ScriptFilter
 propertyset=org.apache.tools.ant.types.PropertySet
+assertion=org.apache.tools.ant.types.Assertion