add handy getter for the File

git-svn-id: https://svn.apache.org/repos/asf/lucene/java/trunk@150226 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/lucene/store/FSDirectory.java

@@ -372,6 +372,10 @@ public final class FSDirectory extends Directory {
     }
   }
 
+  public File getFile() {
+    return directory;
+  }
+
   /** For debug output. */
   public String toString() {
     return "FSDirectory@" + directory;