modified to infer the default value for Hudson URL when none is set.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@2399 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/resources/hudson/tasks/Mailer/global.jelly

@@ -18,7 +18,7 @@
     <f:entry title="Hudson URL"
              help="/help/tasks/mailer/url.html">
       <input class="setting-input" name="mailer_hudson_url"
-        type="text" value="${descriptor.url}"/>
+        type="text" value="${h.ifThenElse(descriptor.url!=null,descriptor.url,h.inferHudsonURL(request))}"/>
     </f:entry>
     <!--f:advanced-->
       <f:optionalBlock name="mailer.useSMTPAuth" title="Use SMTP Authentication" checked="${descriptor.smtpAuthUserName!=null}"