[IMP-dev] algebra::get_unit_bounding_box_d()

algebra::get_unit_bounding_box_d() currently returns a bounding box with diameter 1 (that is, one reaching from 0 to 1 in each coordinate). This isn't documented and is kind of inconsistent with algebra::get_unit_sphere_d() which returns a sphere with radius 1. I'd like to change the former to be consistent (so get_bounding_box(get_unit_sphere_d()) == get_unit_bounding_box_d()). It doesn't look like anything in IMP depends on the old behavior, but it is used in various tests and examples (at least some of which seem to assume the behavior I'd like to change it to). Thoughts? Objections?