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_tt.cpp

@@ -20,7 +20,6 @@ int test_main(int, char* [])
     typedef bg::model::point<ttmath_big, 2, bg::cs::cartesian> P2ttmc;
 
     test_rtree<P2ttmc, bgi::linear<4, 2> >();
-    test_rtree<P2ttmc>(bgi::runtime::linear(4, 2));
 
 #endif