Better error reporting in case a corrupt ZIP file is on the classpath.

Formerly would show a ZipException stack trace but give no indication of which file was responsible.
(Of course it would be better if ZipFile.open itself included the file path in the detail message!)
Cf.: http://www.netbeans.org/nonav/issues/show_bug.cgi?id=142733


git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@683997 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/AntClassLoader.java

@@ -984,6 +984,7 @@ public class AntClassLoader extends ClassLoader implements SubBuildListener {
                 }
             }
         } catch (Exception e) {
+            log("Unable to obtain resource from " + file + ": " + e, Project.MSG_WARN);
             e.printStackTrace();
         }
         return null;