Revert 6f68e52 and fix the gcc2 build via template.

* Instead of forcing the hash-table to use a copy of the key,
  introduce and use TypeOperation template to avoid taking a
  reference of a reference type (which gcc2 doesn't allow).

headers/private/shared/TypeOperation.h

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2014, Haiku, Inc. All Rights Reserved.
+ * Distributed under the terms of the MIT License.
+ *
+ * Based on TypeOp in "C++-Templates, The Complete Guide", which is
+ * Copyright 2003 by Pearson Education, Inc.
+ */
+#ifndef _TYPE_OPERATION_H
+#define _TYPE_OPERATION_H
+
+namespace BPrivate {
+
+
+// Generic type conversion operations.
+template<typename T>
+class TypeOperation {
+public:
+	typedef T					ArgT;
+	typedef T					BareT;
+	typedef T const				ConstT;
+
+	typedef T&					RefT;
+	typedef T&					BareRefT;
+	typedef T const&			ConstRefT;
+};
+
+
+// Specialization for constant types.
+template<typename T>
+class TypeOperation<T const> {
+public:
+	typedef T const				ArgT;
+	typedef T					BareT;
+	typedef T const				ConstT;
+
+	typedef T const&			RefT;
+	typedef T&					BareRefT;
+	typedef T const&			ConstRefT;
+};
+
+
+// Specialization for reference types.
+template<typename T>
+class TypeOperation<T&> {
+public:
+	typedef T&									ArgT;
+	typedef typename TypeOperation<T>::BareT	BareT;
+	typedef T const								ConstT;
+
+	typedef T&									RefT;
+	typedef typename TypeOperation<T>::BareRefT	BareRefT;
+	typedef T const&							ConstRefT;
+};
+
+
+// Specialization for void.
+template<>
+class TypeOperation<void> {
+public:
+	typedef void				ArgT;
+	typedef void				BareT;
+	typedef void const			ConstT;
+
+	typedef void				RefT;
+	typedef void				BareRefT;
+	typedef void				ConstRefT;
+};
+
+
+}	// namespace BPrivate
+
+
+using BPrivate::TypeOperation;
+
+
+#endif	// _TYPE_OPERATION_H