expose unpinning to the web UI.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@34045 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/PluginWrapper.java

@@ -452,6 +452,10 @@ public class PluginWrapper implements Comparable<PluginWrapper> {
     public boolean hasUpdate() {
         return getUpdateInfo()!=null;
     }
+    
+    public boolean isPinned() {
+        return pinFile.exists();
+    }
 
     /**
      * Sort by short name.