Try to make error message clearer

PR:	17033


git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@274089 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/taskdefs/optional/PropertyFile.java

@@ -1,7 +1,7 @@
 /*
  * The Apache Software License, Version 1.1
  *
- * Copyright (c) 2000-2002 The Apache Software Foundation.  All rights
+ * Copyright (c) 2000-2003 The Apache Software Foundation.  All rights
  * reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -533,8 +533,8 @@ public class PropertyFile extends Task {
                     + "properties (key:" + key + ")");
             }
             if (value == null && defaultValue == null) {
-                throw new BuildException("value and/or default must be " 
-                    + "specified (key:" + key + ")");
+                throw new BuildException("\"value\" and/or \"default\" " 
+                    + "attribute must be specified (key:" + key + ")");
             }
             if (key == null) {
                 throw new BuildException("key is mandatory");