Fix/point on surface

Fix for https://svn.boost.org/trac/boost/ticket/10643.

The issue is caused by numerical errors for big FP values in centroid default strategy (bashein_detmer) which internally stores values as big as squares of coordinates.

This PR replaces bashein-detmer with arithmetic mean which applied to extremes should give good results. I plan to add more tests to be sure about it.

If everything was ok should a function `calculate_centroid()` be removed?

As a side note. This shows that a `centroid()` function most certainly doesn't work in all cases but a fix for this function should be a part of other PR.