storage/nfs: move code to class MemoryStorageDirectoryReader

Read all directory entries into memory and close the struct nfsdir
before returning the StorageDirectoryReader instance.  This is what
libnfs does, anyway.

src/storage/MemoryDirectoryReader.cxx

@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "MemoryDirectoryReader.hxx"
+
+#include <assert.h>
+
+const char *
+MemoryStorageDirectoryReader::Read()
+{
+	if (first)
+		first = false;
+	else
+		entries.pop_front();
+
+	if (entries.empty())
+		return nullptr;
+
+	return entries.front().name.c_str();
+}
+
+bool
+MemoryStorageDirectoryReader::GetInfo(gcc_unused bool follow, FileInfo &info,
+				      gcc_unused Error &error)
+{
+	assert(!first);
+	assert(!entries.empty());
+
+	info = entries.front().info;
+	return true;
+}