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/rtree3d_linear_d.cpp

@@ -18,7 +18,6 @@ int test_main(int, char* [])
     typedef bg::model::point<double, 3, bg::cs::cartesian> P3dc;
 
     test_rtree<P3dc, bgi::linear<4, 2> >();
-    test_rtree<P3dc>(bgi::runtime::linear(4, 2));
     
     return 0;
 }