reject IPv6 names. Revisit later as IPv6 should work in theory --- it's just...

reject IPv6 names. Revisit later as IPv6 should work in theory --- it's just that my limited experiment revealed that it doesn't seem to be working

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@17573 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/model/Computer.java

@@ -578,7 +578,7 @@ public /*transient*/ abstract class Computer extends Actionable implements Acces
         for( String address : getChannel().call(new ListPossibleNames())) {
             try {
                 InetAddress ia = InetAddress.getByName(address);
-                if(ia.isReachable(500))
+                if(ia.isReachable(500) && ia instanceof Inet4Address)
                     return ia.getCanonicalHostName();
             } catch (IOException e) {
                 // if a given name fails to parse on this host, we get this error