[FIXED JENKINS-12514]

Fixed the file overwrite problem on Windows.

core/src/main/java/hudson/PluginManager.java

@@ -414,12 +414,9 @@ public abstract class PluginManager extends AbstractModelObject {
         File file = new File(rootDir, fileName);
         File pinFile = new File(rootDir, fileName+".pinned");
 
-        {// normalization first
-            File legacyFile = new File(rootDir,legacyName);
-            if (legacyFile.exists())    legacyFile.renameTo(file);
-            File legacyPinFile = new File(rootDir,legacyName+".pinned");
-            if (legacyPinFile.exists())    legacyPinFile.renameTo(pinFile);
-        }
+        // normalization first, if the old file exists.
+        rename(new File(rootDir,legacyName),file);
+        rename(new File(rootDir,legacyName+".pinned"),pinFile);
         
         // update file if:
         //  - no file exists today
@@ -434,6 +431,20 @@ public abstract class PluginManager extends AbstractModelObject {
         }
     }
 
+    /**
+     * Rename a legacy file to a new name, with care to Windows where {@link File#renameTo(File)}
+     * doesn't work if the destination already exists.
+     */
+    private void rename(File legacyFile, File newFile) throws IOException {
+        if (!legacyFile.exists())   return;
+        if (newFile.exists()) {
+            Util.deleteFile(newFile);
+        }
+        if (!legacyFile.renameTo(newFile)) {
+            LOGGER.warning("Failed to rename " + legacyFile + " to " + newFile);
+        }
+    }
+
     /**
      * Creates a hudson.PluginStrategy, looking at the corresponding system property. 
      */