Do not allow options in filesystem clearContainer

This requires some additional logic to clean up empty directories.
Test regression from 22ce5484a412bc06ef62995675c07e7a85f66bdf.
diff --git a/apis/filesystem/src/main/java/org/jclouds/filesystem/strategy/internal/FilesystemStorageStrategyImpl.java b/apis/filesystem/src/main/java/org/jclouds/filesystem/strategy/internal/FilesystemStorageStrategyImpl.java
index 733b1f0..211cb42 100644
--- a/apis/filesystem/src/main/java/org/jclouds/filesystem/strategy/internal/FilesystemStorageStrategyImpl.java
+++ b/apis/filesystem/src/main/java/org/jclouds/filesystem/strategy/internal/FilesystemStorageStrategyImpl.java
@@ -17,6 +17,7 @@
 package org.jclouds.filesystem.strategy.internal;
 
 import static com.google.common.base.Charsets.US_ASCII;
+import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.common.base.Strings.isNullOrEmpty;
 import static com.google.common.io.BaseEncoding.base16;
@@ -252,9 +253,8 @@
    @Override
    public void clearContainer(String container, ListContainerOptions options) {
       filesystemContainerNameValidator.validate(container);
-      if (options.getDir() != null) {
-         container += denormalize("/" + options.getDir());
-      }
+      // TODO: these require calling removeDirectoriesTreeOfBlobKey
+      checkArgument(options.getDir() == null || options.getPrefix() == null, "cannot specify directory or prefix");
       try {
          File containerFile = openFolder(container);
          File[] children = containerFile.listFiles();
diff --git a/apis/filesystem/src/test/java/org/jclouds/filesystem/integration/FilesystemContainerIntegrationTest.java b/apis/filesystem/src/test/java/org/jclouds/filesystem/integration/FilesystemContainerIntegrationTest.java
index 7dfdd3a..c9fee73 100644
--- a/apis/filesystem/src/test/java/org/jclouds/filesystem/integration/FilesystemContainerIntegrationTest.java
+++ b/apis/filesystem/src/test/java/org/jclouds/filesystem/integration/FilesystemContainerIntegrationTest.java
@@ -193,4 +193,9 @@
    public void testSetContainerAccess() throws Exception {
       throw new SkipException("filesystem does not support anonymous access");
    }
+
+   @Override
+   public void testClearWithOptions() throws InterruptedException {
+      throw new SkipException("filesystem does not support clear with options");
+   }
 }