External monitor job type is moved to a plugin.

The actual release needs to happen in a lock step, as the new plugin
needs to require yet-to-be-released version of the core. So for the time
being it's a snapshot dependency, deployed in the snapshot repository.

core/src/main/java/hudson/ClassicPluginStrategy.java

@@ -245,7 +245,8 @@ public class ClassicPluginStrategy implements PluginStrategy {
         new DetachedPlugin("subversion","1.310","1.0"),
         new DetachedPlugin("cvs","1.340","0.1"),
         new DetachedPlugin("ant","1.430.*","1.0"),
-        new DetachedPlugin("javadoc","1.430.*","1.0")
+        new DetachedPlugin("javadoc","1.430.*","1.0"),
+        new DetachedPlugin("external-monitor-job","1.467.*","1.0")
     );
 
     /**