Import cpp-btree library into 3rdparty section.

Repo: https://github.com/JGRennison/cpp-btree
Commmit: 6cabdb40fcbb7e12e6d499f92b898f6ec80ae0f1

Remove test program, build scripts, etc.

src/3rdparty/cpp-btree/btree_set.h

@@ -0,0 +1,145 @@
+// Copyright 2013 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// A btree_set<> implements the STL unique sorted associative container
+// interface (a.k.a set<>) using a btree. A btree_multiset<> implements the STL
+// multiple sorted associative container interface (a.k.a multiset<>) using a
+// btree. See btree.h for details of the btree implementation and caveats.
+
+#ifndef UTIL_BTREE_BTREE_SET_H__
+#define UTIL_BTREE_BTREE_SET_H__
+
+#include <functional>
+#include <memory>
+#include <string>
+
+#include "btree.h"
+#include "btree_container.h"
+
+namespace btree {
+
+// The btree_set class is needed mainly for its constructors.
+template <typename Key,
+          typename Compare = std::less<Key>,
+          typename Alloc = std::allocator<Key>,
+          int TargetNodeSize = 256>
+class btree_set : public btree_unique_container<
+  btree<btree_set_params<Key, Compare, Alloc, TargetNodeSize> > > {
+
+  typedef btree_set<Key, Compare, Alloc, TargetNodeSize> self_type;
+  typedef btree_set_params<Key, Compare, Alloc, TargetNodeSize> params_type;
+  typedef btree<params_type> btree_type;
+  typedef btree_unique_container<btree_type> super_type;
+
+ public:
+  typedef typename btree_type::key_compare key_compare;
+  typedef typename btree_type::allocator_type allocator_type;
+
+ public:
+  // Default constructor.
+  btree_set(const key_compare &comp = key_compare(),
+            const allocator_type &alloc = allocator_type())
+      : super_type(comp, alloc) {
+  }
+
+  // Copy constructor.
+  btree_set(const self_type &x)
+      : super_type(x) {
+  }
+
+  // Move constructor.
+  btree_set(self_type &&x)
+      : super_type() {
+    this->swap(x);
+  }
+
+  // Copy/move assignment
+  self_type& operator=(self_type x) {
+    this->swap(x);
+    return *this;
+  }
+
+  // Range constructor.
+  template <class InputIterator>
+  btree_set(InputIterator b, InputIterator e,
+            const key_compare &comp = key_compare(),
+            const allocator_type &alloc = allocator_type())
+      : super_type(b, e, comp, alloc) {
+  }
+};
+
+template <typename K, typename C, typename A, int N>
+inline void swap(btree_set<K, C, A, N> &x, btree_set<K, C, A, N> &y) {
+  x.swap(y);
+}
+
+// The btree_multiset class is needed mainly for its constructors.
+template <typename Key,
+          typename Compare = std::less<Key>,
+          typename Alloc = std::allocator<Key>,
+          int TargetNodeSize = 256>
+class btree_multiset : public btree_multi_container<
+  btree<btree_set_params<Key, Compare, Alloc, TargetNodeSize> > > {
+
+  typedef btree_multiset<Key, Compare, Alloc, TargetNodeSize> self_type;
+  typedef btree_set_params<Key, Compare, Alloc, TargetNodeSize> params_type;
+  typedef btree<params_type> btree_type;
+  typedef btree_multi_container<btree_type> super_type;
+
+ public:
+  typedef typename btree_type::key_compare key_compare;
+  typedef typename btree_type::allocator_type allocator_type;
+
+ public:
+  // Default constructor.
+  btree_multiset(const key_compare &comp = key_compare(),
+                 const allocator_type &alloc = allocator_type())
+      : super_type(comp, alloc) {
+  }
+
+  // Copy constructor.
+  btree_multiset(const self_type &x)
+      : super_type(x) {
+  }
+
+  // Move constructor.
+  btree_multiset(self_type &&x)
+      : super_type() {
+    this->swap(x);
+  }
+
+  // Copy/move assignment
+  self_type& operator=(self_type x) {
+    this->swap(x);
+    return *this;
+  }
+
+  // Range constructor.
+  template <class InputIterator>
+  btree_multiset(InputIterator b, InputIterator e,
+                 const key_compare &comp = key_compare(),
+                 const allocator_type &alloc = allocator_type())
+      : super_type(b, e, comp, alloc) {
+  }
+};
+
+template <typename K, typename C, typename A, int N>
+inline void swap(btree_multiset<K, C, A, N> &x,
+                 btree_multiset<K, C, A, N> &y) {
+  x.swap(y);
+}
+
+} // namespace btree
+
+#endif  // UTIL_BTREE_BTREE_SET_H__