applied patch for #448 from Valeri.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@4242 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/FilePath.java

@@ -455,6 +455,17 @@ public final class FilePath implements Serializable {
             }
         });
     }
+    
+    /**
+     * Returns the file size in bytes.
+     */
+    public long length() throws IOException, InterruptedException {
+        return act(new FileCallable<Long>() {
+            public Long invoke(File f, VirtualChannel channel) throws IOException {
+                return f.length();
+            }
+        });
+    }
 
     /**
      * List up files in this directory.