rtree: order of includes matters

[daniel-j-h]

I'm currently testing the new Boost 1.62 Beta1 release. Including the rtree header before the parameters header works fine. For the other way around I get errors; here's the first one:

include/boost/geometry/index/parameters.hpp:76:26: error: expected identifier before ‘(’ token

Small self-contained test case:

#include <boost/geometry/index/parameters.hpp>
#include <boost/geometry/index/rtree.hpp>

int main() {}

Found this since I'm using clang-format and recent versions re-order includes alphabetically.

[awulkiew]

Thanks!
Fix: b8b1cc5