Added include missing file with forward declarations.

common/forwardDeclarations.hpp

+/*
+ * The CERN Tape Archive (CTA) project
+ * Copyright (C) 2015  CERN
+ *
+ * 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 3 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, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+namespace cta {
+// Forward declarations for opaque references.
+namespace common {
+namespace admin {
+  class AdminHost;
+  class AdminUser;
+} // cta::common::admin
+namespace archiveNS {
+  class ArchiveFile;
+  class ArchiveDirIterator;
+  class ArchiveFileStatus;
+} // cta::common::archiveNS 
+namespace archiveRoute {
+  class ArchiveRoute;
+} // cta::common::archiveRoute
+} // cta::common
+class ArchiveToFileRequest;
+class ArchiveToTapeCopyRequest;
+class LogicalLibrary;
+class NameServer;
+class RemoteNS;
+class RemotePathAndStatus;
+class RetrieveRequestDump;
+class RetrieveToFileRequest;
+class SchedulerDatabase;
+class SecurityIdentity;
+class StorageClass;
+class Tape;
+class TapeMount;
+class TapeSession;
+class TapePool;
+class UserIdentity;
+} /// cta
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