[IO-634] Make getCause synchronized and use a Deque instead of Stack (#64)

* Fix "Non-synchronized override of synchronized method".

* Replace synchronized Stack with unsynchronized Deque in FilenameUtils.

Author: wilx

src/main/java/org/apache/commons/io/FilenameUtils.java

@@ -18,11 +18,12 @@
 
 import java.io.File;
 import java.io.IOException;
+import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.Deque;
 import java.util.List;
-import java.util.Stack;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -1385,11 +1386,11 @@ public static boolean wildcardMatch(final String fileName, final String wildcard
         boolean anyChars = false;
         int textIdx = 0;
         int wcsIdx = 0;
-        final Stack<int[]> backtrack = new Stack<>();
+        final Deque<int[]> backtrack = new ArrayDeque<>(wcs.length);
 
         // loop around a backtrack stack, to handle complex * matching
         do {
-            if (backtrack.size() > 0) {
+            if (!backtrack.isEmpty()) {
                 final int[] array = backtrack.pop();
                 wcsIdx = array[0];
                 textIdx = array[1];
@@ -1448,7 +1449,7 @@ public static boolean wildcardMatch(final String fileName, final String wildcard
                 return true;
             }
 
-        } while (backtrack.size() > 0);
+        } while (!backtrack.isEmpty());
 
         return false;
     }

src/main/java/org/apache/commons/io/TaggedIOException.java

@@ -129,7 +129,7 @@ public Serializable getTag() {
      * @return wrapped exception
      */
     @Override
-    public IOException getCause() {
+    public synchronized IOException getCause() {
         return (IOException) super.getCause();
     }