include the caught exception when relayed

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@381998 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/taskdefs/optional/net/FTP.java

@@ -2348,7 +2348,7 @@ public class FTP
             }
 
         } catch (IOException ex) {
-            throw new BuildException("error during FTP transfer: " + ex);
+            throw new BuildException("error during FTP transfer: " + ex,ex);
         } finally {
             if (ftp != null && ftp.isConnected()) {
                 try {