This change broke JNLPLauncherTest by hiding JNLP launch link.

So for now I'm chaging the implementation so that it hides launcher main.jelly if and only the strategy demands to do so,
which is closer to Stephen's original intention (even though this makes the method somewhat inconsistent with its name.)  
 
I'm of opinion that we shouldn't try to hide the launcher, but I'm waiting for Stephen to chime in on that change.
See http://www.nabble.com/Re%3A-svn-commit%3A-r14467---trunk-hudson-main-core-src-main%3A-java-hudson-model-java-hudson-slaves-resources-hudson-model-Computer-tt21465182.html

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@14488 71c3de6d-444a-0410-be80-ed276b4c234a

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

@@ -246,7 +246,7 @@ public abstract class Computer extends AbstractModelObject implements AccessCont
      */
     @Exported
     public boolean isManualLaunchAllowed() {
-        return getRetentionStrategy().isManualLaunchAllowed(this) && isLaunchSupported();
+        return getRetentionStrategy().isManualLaunchAllowed(this);
     }
 
 
@@ -266,7 +266,11 @@ public abstract class Computer extends AbstractModelObject implements AccessCont
     }
 
     /**
-     * Returns true if this computer can be launched by Hudson.
+     * Returns true if this computer can be launched by Hudson proactively and automatically.
+     *
+     * <p>
+     * For example, JNLP slaves return {@code false} from this, because the launch process
+     * needs to be initiated from the slave side.
      */
     @Exported
     public boolean isLaunchSupported() {