Merged from index_dev

Fixed rtree::clear() mem leak.
Added test for clear() and boost::shared_ptr as Values.
Each linear algo test file divided into 2 files.
Added reference in docs->rtree introduction.

[SVN r81778]

test/rtree/rtree2d_linear_d_rt.cpp

@@ -0,0 +1,23 @@
+// Boost.Geometry Index
+// Unit Test
+
+// Copyright (c) 2011-2012 Adam Wulkiewicz, Lodz, Poland.
+
+// Use, modification and distribution is subject to the Boost Software License,
+// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#include <rtree/test_rtree.hpp>
+
+#include <boost/geometry/geometries/point_xy.hpp>
+#include <boost/geometry/geometries/point.hpp>
+#include <boost/geometry/geometries/box.hpp>
+
+int test_main(int, char* [])
+{
+    typedef bg::model::point<double, 2, bg::cs::cartesian> P2dc;
+
+    test_rtree<P2dc>(bgi::runtime::linear(4, 2));
+    
+    return 0;
+}