[index][strategies][test] Modify some of the header includes.

The purpose of this is to allow the compilation of the rtree without the need of including the geometry.hpp ond require only index/rtree.hpp or to make the order of includes irrelevant.
Furthermore, this is backward compatible.

Add missing variant include in the intersection tests.
Fix the unused typedefs in the pythagoras_point_box test.

include/boost/geometry/index/rtree.hpp

@@ -12,17 +12,15 @@
 #ifndef BOOST_GEOMETRY_INDEX_RTREE_HPP
 #define BOOST_GEOMETRY_INDEX_RTREE_HPP
 
+// STD
 #include <algorithm>
 
+// Boost
 #include <boost/tuple/tuple.hpp>
 #include <boost/move/move.hpp>
 
-//#include <boost/geometry/geometry.hpp>
-// START
-#include <boost/geometry/strategies/strategies.hpp>
-
-#include <boost/geometry/algorithms/comparable_distance.hpp>
-#include <boost/geometry/algorithms/distance.hpp>
+// Boost.Geometry
+#include <boost/geometry/algorithms/detail/comparable_distance/interface.hpp>
 #include <boost/geometry/algorithms/centroid.hpp>
 #include <boost/geometry/algorithms/covered_by.hpp>
 #include <boost/geometry/algorithms/disjoint.hpp>
@@ -34,8 +32,10 @@
 
 #include <boost/geometry/geometries/point.hpp>
 #include <boost/geometry/geometries/box.hpp>
-// END
 
+#include <boost/geometry/strategies/strategies.hpp>
+
+// Boost.Geometry.Index
 #include <boost/geometry/index/detail/config_begin.hpp>
 
 #include <boost/geometry/index/detail/assert.hpp>
@@ -1798,6 +1798,9 @@ inline void swap(rtree<Value, Parameters, IndexableGetter, EqualTo, Allocator> &
 
 }}} // namespace boost::geometry::index
 
+// TODO: don't include the implementation at the end of the file
+#include <boost/geometry/algorithms/detail/comparable_distance/implementation.hpp>
+
 #include <boost/geometry/index/detail/config_end.hpp>
 
 #endif // BOOST_GEOMETRY_INDEX_RTREE_HPP

include/boost/geometry/strategies/cartesian/centroid_weighted_length.hpp

@@ -13,7 +13,8 @@
 #ifndef BOOST_GEOMETRY_STRATEGIES_CARTESIAN_CENTROID_WEIGHTED_LENGTH_HPP
 #define BOOST_GEOMETRY_STRATEGIES_CARTESIAN_CENTROID_WEIGHTED_LENGTH_HPP
 
-#include <boost/geometry/algorithms/distance.hpp>
+#include <boost/geometry/algorithms/detail/distance/interface.hpp>
+#include <boost/geometry/algorithms/detail/distance/point_to_geometry.hpp>
 #include <boost/geometry/arithmetic/arithmetic.hpp>
 #include <boost/geometry/util/select_most_precise.hpp>
 #include <boost/geometry/strategies/centroid.hpp>

test/algorithms/test_intersection.hpp

@@ -14,6 +14,7 @@
 
 #include <boost/core/ignore_unused.hpp>
 #include <boost/foreach.hpp>
+#include <boost/variant/variant.hpp>
 
 #include <boost/geometry/algorithms/intersection.hpp>
 #include <boost/geometry/algorithms/area.hpp>

test/strategies/pythagoras_point_box.cpp

@@ -27,6 +27,7 @@
 #  pragma warning( disable : 4101 )
 #endif
 
+#include <boost/core/ignore_unused.hpp>
 #include <boost/timer.hpp>
 #include <boost/typeof/typeof.hpp>
 
@@ -184,6 +185,12 @@ inline void test_services()
             <
                 bg::box_tag, bg::point_tag, Box, Point
             >::type reversed_pythagoras_pb_strategy_type;
+
+        boost::ignore_unused
+            <
+                pythagoras_pb_strategy_type,
+                reversed_pythagoras_pb_strategy_type
+            >();
     }
 
     Point p;