Fix/disjoint

PR fixing Areal/Areal version by replacing `point_on_surface()` with `point_on_border()` and `within()` with `covered_by()` for backward compatibility (https://svn.boost.org/trac/boost/ticket/8310).

Related to https://github.com/boostorg/geometry/pull/159 and https://github.com/boostorg/geometry/pull/162.

I agree that `for_each_range_if()` would be a useful thing to have. Also `for_each_point()` and `for_each_segment()` could use an `..._if()` analogue.
But for now and given the release schedule, this is not feasible.

About `||=`: by bad. You get the point though.