improve FTP support

- allow to disable active mode
- allow to disable SITE commands
- add optional support for calculating hash value of files
- add optional support for the non standard COMB command

webdavd/internal_test.go

@@ -752,6 +752,9 @@ func TestBasicUsersCache(t *testing.T) {
 	assert.NoError(t, err)
 	_, ok = dataprovider.GetCachedWebDAVUser(username)
 	assert.False(t, ok)
+
+	err = os.RemoveAll(u.GetHomeDir())
+	assert.NoError(t, err)
 }
 
 func TestUsersCacheSizeAndExpiration(t *testing.T) {
@@ -934,6 +937,9 @@ func TestUsersCacheSizeAndExpiration(t *testing.T) {
 	assert.NoError(t, err)
 	err = dataprovider.DeleteUser(user4)
 	assert.NoError(t, err)
+
+	err = os.RemoveAll(u.GetHomeDir())
+	assert.NoError(t, err)
 }
 
 func TestRecoverer(t *testing.T) {